"But beyond that... not every bug needs fixing; that's a trap"
this doesn't seem good attitude for critical software like database
I do tend to agree with this ( i write database internals and engines for a living _). Letting software accumulate even little bugs is not a good look. Yes prioritize but definitely don't leave the smaller things, they will just pile up and make next work even harder.
Old bugs are sometimes undesirable to fix because other systems/users have come to rely on their behavior.
the optimal amount of fraud for a fintech is non-zero
why would the optimal amount of bugs be anything less for a database?
Not every part of a critical piece system is itself critical.
Seatback entertainment in aircraft are not critical. Aircraft are.
In Postgres, there are plenty low-priority, low-impact bugs. #16265, for instance, reports that the capitalization of a relation in an error message is confusing. The report got mostly ignored. And that seems not a great loss.
Dare I say, solving every bug does not make economic sense.