Former English teacher here. My self-hosting origin is that I had 20 years or so of teaching materials I'd collected in OneNote over that time and simply wanted to have offline copies so that I could feel that if ever something went wrong with Microsoft like getting permanently locked out of my account, then I had a means of restoring everything. Microsoft makes it practically impossible to export to a working backup.
After spending a LONG time trying everything to get back ownership of my materials, I understood the need to move my digital stuff away from big tech. I bought a Synology NAS, learned how to use Docker and then took more steps. About the same time I started using Fediverse apps and learned a great deal from the discussions and links there. My greatest "learn" has been keeping notes in plaintext files (and not getting seduced by nice shiny new apps that are actually horrors that want lure you into a future subscription).
I did make the jump... into unemployment. But still much happier. I love teaching and would join an authentic, child-centred school at the drop of a hat - but not willing to be complicit in the toxic horror show that's current UK education.