What I just showed probably isn't much of a problem for most people, since they won't care all that much about the quality of an image as long as they can still view it. At that point, it starts getting harder to convince people that trusting their media with other services is a bad idea. But media compression isn't the only argument against using services you don't control to host your media. In fact, I think it's reasonable to say it's not even the most convincing.
When you upload something to Google Photos, for example, you have no idea what it does to the file you just sent it. The things we do know that Google Photos does should be disturbing to a lot of people. It analyzes all photos uploaded to it with AI image recognition to label it, and will try to organize your photos based on it if you wish. Is it not disturbing that a giant company like Google would analyze all of your photos, no matter what they are? If that still doesn't matter to you, then consider the following.
It's pretty self-explanatory, the bigger the service, the more people will be trying to break into it. That's not the fault of the services, but it has the ability to affect you. And this has happened before, at a large scale. Services as large and secure as iCloud have been hacked before, and caused giant scandals like having celebrity photos leaked publicly. It'd be unfair to say that these services are less secure than a self-hosted solution, but they have the massive disadvantage of being giant targets, and again, you have less control and have to rely on their security and decisions.
Giving other people your files means that they have the power to delete them. Since they are actually the ones who own the files, they have ultimate power over them, and often they exercise this power. For example, it's very common for storage services to delete porn. If you want to reliably store all of your media, you can't use a service that exercises their own arbitrary rules over your files. Want to see this in action for yourself? If you have a YouTube account (virtually everyone does, since they have a Google account), go upload a copyrighted music video and see what happens. The video will be taken down or have restrictions applied to it.
(Don't actually do that since you can get your account in trouble if you do.)
Let's say you have a 20mb
raw photo file. It's unlikely that you will be able to upload this to any typical image hosting service, since they only accept images processed into typical image formats. Or, how about you have a 2 hour video you would like to upload to YouTube. Unless you've given YouTube your phone number, you will be unable to upload the video. But let's say you do have a phone number linked, and you upload it successfully. Your YouTube upload will be watchable, but YouTube provides no features for viewers of your video to download it, and something like that can only be done with special software like
youtube-dl. Services often place restrictions on how you can use or distribute your files, and issues like that can be fixed if you host your media on your own.
Since I host my own media, I can offer people downloads of videos very easily. To save this video, just right click and hit "Save video as".
Remember when I said that services such as Google Photos analyze your photos? If every photo or video you post is processed and analyzed by a server, it becomes very trivial to make automated assumptions about you. I'm not even talking about the possibility of some staff of one of those services looking at your photos, the chance of something like that happening is incredibly low, but the possibility of automated systems making connections about you is much, much higher, and more dangerous since it can be done at a massive scale, and be done on people that normally wouldn't be of interest to actual people.
