

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.
Without technical know-how or experience in general using NAS, Synology is a good first-time option. All apps are ready for immediate use. And don’t forget the majority of computer users don’t even know what a NAS is and they simply want to store files for remote access.