JohnP brought next idea :
Tirning the tap more just ends up deforming the washer into the seating.
The washer is just like a lid - pressed "on" should be enough. Tightening
it more only ends up wrecking the washer and wearing the threads.

Yep, me too. Some see the spout dripping after it's off, as a need to
give it an extra 1/2 turn, whereas it is just the spout draining. The
cold usually does this, as the cold water warms up and expands.