I think a big portion of this isn't a difference in quality, but rather complexity. Postgres is just easier to understand than Oracle. Oracle has insane amounts

I think a big portion of this isn't a difference in quality, but rather complexity. Postgres is just easier to understand than Oracle. Oracle has insane amounts of settings and configurable parts. The end result is that people who admin postgres servers tend to learn the levers, but many Oracle DBAs simply don't, or have environments where hand tuning is really hard to justify time-wise. I think Postgres success is it's often in environments where DBAs and devs work closely or are the same person.