Personal users want E2E encyrption, so it doesn't matter who is running the server. And most users do not have the skill to run their own server. The technically advanced can just use the enterprise version if they really care about personal on prem.
Maybe we should change the notion that it's difficult to deploy an on prem service.
Why can't it be as simple as containerizing it and presenting it exactly like your would install an app on your phone, with the same possibility to grant permissions? App store provides automatic OTA updates so you don't have to bother about security. And the app itself should not have internet connectivity, connectivity is provided through authenticated tunnel into the container so the app cannot phone home in the background, you can only connect into it using the tunnel with your own password.
Even if you have the skill, is it worth the time to do on-prem, considering, you know, a pen and paper?
(Full disclosure: I'm a total bullet journaling convert. Given a choice between giving up my bullet journal and giving up Google Calendar/Docs and Trello, I'd give up the online stuff in a heartbeat.)
