There are three reasons that I can think of:
- Privacy
- Collaboration
- Accessibility / cost
Privacy. This is obvious. People don’t want their private information to be sold by corporations or scraped by AI.
Collaboration To share information with others, while maintaining point 1, people have to self host. Say, you want to archive a bunch of photos for personal viewing then you can store them anywhere you like. But if you want to share them with family, a self hosted solution is the way to go.
Accessibility / cost People want to do things for free. Many applications offer free version or demo, but features are often limited and you can’t really customize them to your own needs. In addition, applications often adopt a subscription model these days and people don’t like that.
To answer your question, most people don’t have just one device. Do you have only one device? You must have at least a desktop computer and a smartphone? What if you want to have something stored in your computer when you are not at home?
Music for example. If I don’t want to pay Spotify or whatever, and I want to listen to my music on my phone at work and on my computer at home. Other than making two full copies of the entire music library, I think I have to store them on a 3rd location then share it to my two devices.
If I don’t listen to music at home, then you’re right, there’s no reason to self host anything. I can just store all songs on my phone.