My understanding their stack is Python. So they probably have high costs as well :)
Sentry is python and has extremely reasonable costs (and you can even self-host it).
Honestly if you want to complain at the cost of hosting (which, we don't know if they would) then licensing the software and allowing people to self-host would be the solution.
$65M is enough that I could fund a team running google's monarch system for 7-8 years.
I thought Sentry was Ruby?
You can take a look at the Python codebase for Sentry over here: https://github.com/getsentry/sentry
There's rust stuff too: https://github.com/getsentry/relay