Cloud storage is what I do for a living and I do everything I can to avoid using "the cloud" whenever feasible. Look, "the cloud" just means someone else's computer. And since it's someone else's computer, that means they can change how it works, where it is, who has access to it, and what you're going to have to pay for it without a whole lot of consent from you. As an aside, sit down and actually read your medical providers' HIPAA statements that you always just sign off that you've received them when you probably haven't. I don't know the exact number, but in my own reading, almost all of them say that your doctor can share your personal medical information with law enforcement upon request. Not upon being served a warrant. Upon *request*. Pretty cool, huh? Not really the point, but it is tangentially related to the conversation at hand since the provider of the cloud service is not really all that interested in your privacy, they're more interested in saving themselves hassle and headache from police, politicians, and bad press. And nobody gets bad press because they gave someone with a badge access to your private data without a warrant; they get bad press because a guy with a badge needed information to save little Patty Sue and the Big Bad Tech company wouldn't just let them snoop through all the information that they wanted.
That's enough of that particular soapbox - I could rant for hours on that until I'm frothy at the mouth. The other issue that you've pointed out is that the cloud provider could pull up stakes and just shut down without any particular warning. Or they could sell the business, of which your contract with them is an asset, and now your data is stored by someone that you did not, perhaps, choose. Basically, you have no control over the lifecycle of someone else's computer, so you could be scrambling to move your data or you may just find some day that your data is just gone. Slightly related to that is access control and encryption. If you're putting your data in some sort of cloud, you should absolutely ensure that you've got some sort of encryption to reduce the impact of the privacy concerns. The downside is that you'd better be sure that you don't lose either of those because your cloud provider won't be able to help you with that - if you lose the key, you lose the data.
Another concern for cloud is access, but this depends entirely on against what you are trying to protect. If it's in the cloud, then you're going to need the Internet to be working in order to get to your data. For personal stuff, that may not be a big deal - if the fit hits the shan and your computer is toast and your Internet access is going to be down for a few days, you may not care that you can't get your document archive.
Gee, Bill, you're painting an awfully dark cloud here, didn't your mom teach you what to do if you don't have something nice to say? Okay, there are some significant benefits out there, I'll admit to that - which I suppose I should since my livelihood currently depends on people buying into this stuff. First of all, it's someone else's computer. If you're a multi-national conglomerate, then you probably have the resources and wherewithal to build out highly-available, highly-scalable compute, network, and storage resources wherever you need them and then maintain them to the highest levels of availability and performance. If you're one of the other 8,199,999,000 people in the world, however, you can benefit from the scale that the cloud provider is able to provide. They're going to have availability zones, fully redundant hardware, generator-backed, redundant power, multi-ingress Internet, and a massive staff who will make sure everything is operating as it should. Yes, there are outages in the cloud and yes, when they happen, they are very impactful because it's not just one business that is affected. But given the sheer number of workloads that are running in those datacenters, it's actually pretty rare and the outages tend to be relatively short. The final bonus in that is that you're not the one that has to go figure out how to fix it - that's the cloud provider's problem.
Speaking of the cloud provider, that makes a big difference as well. If you're buying the Backupatron 9000 service that just entered the marketplace and is making a big splash, there's a good chance they're going to fold in a short time and you'll be out of luck. If you're going to use Google Drive/GCP, OneDrive/Azure, or Amazon's whatevertheydo/S3, then those are more likely to be around for the foreseeable future. Those platforms are going to have a much wider application support base as well, but one nice feature is that Amazon went off and basically created the market and made their S3 API available to the world. That means that if you've got a cloud storage provider they can probably speak S3 which means your application designed for Amazon can probably be configured to speak to that other cloud provider.
Another big benefit is that if you're sending data into a cloud service, you have site-level protection the very moment that data is sent. You don't need to finish a copy to a removable drive and then remember to physically move it somewhere. That means that you can completely automate the process so that your data goes off-site right away, automagically, and you never have to worry that you didn't get the external drive to the fire safe or to the remote, undisclosed bunker before disaster strikes. It also means that the only thing you need to get to your data is a computer and an Internet connection. Not your computer and your connection, but any and any. As long as you've kept your credentials secured - you are using a good password manager, right? - you'll be able to access your data from anywhere.
Okay, that's a lot of theory stuff, but what about actual practice? What does the cloud-hating cloud-guy do to backup his data?
Uhm. I use the cloud. Sort of.
I found a bit of Free software called Duplicati. It installs on my Windows desktop and has a web-browser interface that I use to manage it. I have pointed it to a S3-compatible cloud source that I've got access to. It encrypts the data before upload so that I don't have to worry that anyone would be able to do anything with my data in the event that my bucket is compromised, and I have it set to perform the backup once a day and retain a number of copies so I can go back a day, week, month, or year. It uses compression and deduplication to reduce the amount of cloud storage that I'm consuming - with all of my retentions, I'm using 850GiB to maintain 9 copies of just under 1 TiB of source data. You can point that to any S3-compatible cloud provider - AWS S3 is just over two cents a gig or $20/TiB per month, and it's not likely that you'd incur a large amount of transfer fees for normal backup usage. If you needed to perform a large-scale backup, you'd likely incur some cost for that.
If you wanted to have those files just preserved, you could use something like OneDrive, but now you're trusting Microsoft with the primary copy of all that data and as far as I'm aware, there isn't a good way to self-encrypt that data such that Microsoft doesn't hold the keys.