[eqvinox]

It's because postgres is in fact good at a lot of vaguely database-looking things. Even if it weren't the best for anything, if it does 80% of things at 80% best possible — it is reasonable to have postgres as "first thing to reach for" by default.

That said, it's easy to forget to check if you're in either of those 20% (or both.) There's probably a whole bunch of postgres usage where really something else should be used, and people just never checked.