I'm trying to run my own services. I almost always had my sites on my own server or at the very least web hosting. Years ago I had my own CMS written in PHP, nowadays I'm relying on WordPress and pelican.
Years ago, I also had my own analytics and for reliability reasons switched to Google Analytics. But now I am trying to run plausible on my own server. Sure, there are errors. But the data is mine and since I am not relying on it, I can as well try things out. I am not an IT expert, but nobody's firing me for that.
It started small and cute, but I am also running nextcloud server for my personal files especially my Obsidian vault and Jellyfin on my old computer I use as a homeserver, to listen to audio-books at night.
I am looking for other services to try out, there was Traggo when I needed to keep track of my workhours (I didn't like it much. Now I'm thinking about either writing my own software or setting up TimeTagger). There is Freshrss for keeping up with news (it's a substitute for feedly which I used before). Actually, I might just move that to nextcloud one day if I can make the right plugin working.
I also experiment with things - postiz for scheduling social media posts (I really do not need to do that, I don't post on social media), grocy for home management (I had troubles with that one, but it sounds awesome...).
The reason for all this work is twofold. On one hand, I like to experiment with things. I am a tinkerer when it comes to computers, cosplaying as an admin. The other is paranoia. You can get locked out of your accounts, they might be not available, or just plainly stealing your data for their use.
Did you know that even if you host your data at microsoft's european servers, they will let US government access it? Doesn't bother me, they can read anything I write. But imagine being a company or government - how much will you trust foreign government not to peak? And if a time comes when you do not trust them, I want to know the alternatives.
There might be another reason in that I am cheap skin, but given how much VPS costs and how often services like feedly or google docs are free, It doesn't sound right. Although I did originally subscribe for plausible, which is GDPR friendly, before trying it on my own server. Well, moving it fully, but it does crash on me on occasions.
In my ideal world, I would have everything on my nextcloud (including bookmarks, rss and notes), with libreoffice in their collabora online development edition. With a time tracker, invoice maker, personal finance tool...
Jellyfin at home can have all my former DVDs and CDs on a drive, accessible to listening 24/7. I abuse audiobooks part of it, since I can't fall asleep without a fairy tale (Harry Potter series or Discworld series are my favourites, nothing works as good to me).
The fact that there are so many uses for your own server is probably the best answer to why self-host. Because we can. Because we can be self-reliant. Because we can take charge of our destiny. Because we do not have to surrender our data to advertisers (now that I mentioned it, there is a space for a pi-hole at my home).
For the same reasons we grow our own herbs and other food, we should self-host. For a little bit of independence and little less subscription fees.