Nobody does actually. Postgres not having deterministic query plans is a big pain and a good reason not to use it. The same query may use different query plans depending on the estimated number of affected rows, very frustrating.
Postgresql doesn't have this, however, I've rarely missed this feature - tables with good indexes, regular db hygiene, etc, almost always perform excellently. The query planner is very, very smart nowadays.
There's DB internals/performance course which I'm a TA for and we lean heavily on being able to force Oracle's rule-based or cost-based optimisers --- because then we can get the students to analyse and compare the plans.
As a user, postgres is a far more ergonomic database, but things like this show good old insane oracle is still strongly ahead on some of these points.
In practice, postgres is not as bad as you'd expect in the large, but it can still be anoying.