You probably need to make a request to Izzy. From what I remember he has requirements, such as max app size, which makes me wonder if maybe the ProtonMail app just became too big for him to build and host.
Here are the requirements: https://gitlab.com/IzzyOnDroid/repo/-/wikis/Inclusion%20Policy
It's probably because Proton changed the repo. I was grabbing their release via Obtainium and noticed the version I had was way older than the version on the Play Store. Had to update my Obtainium entry for ProtonMail to the new repo: https://github.com/ProtonMail/android-mail
I was/am in the same boat, but I quickly gave up for the following reason: Why bust my ass trying to give my business? If Lowes blocks me then f*ck em I'll take my business to Home Depot. It's their loss.
For the known top trackers, it's to have more control over nefarious users such as duped accounts, banned users and potential law enforcement trying to sign up. Sure it's not a bulletproof solution to deal with bad actors but it's still an effective way. You gotta remember that these trackers are free (yet private). The admins/operators don't get paid, so last thing they want to do is waste time dealing with such users.
At the end of the day you still have to trust them with your real IP, but it's mostly to protect themselves afaik. I obviously can't speak for every tracker out there.