Platforming gauntlets like that don’t mesh well with the Metroidvania style when used in bulk. Metroidvania corridors are designed to be explored multiple times with multiple exits; making regular rooms difficult to traverse would be pretty annoying.
PoP was fun, but only having it in a single optional area was a good move.
Besides, there are a lot of hardcore platformers out there. Celeste comes to mind.
I just really like all of the movement options in hollow knight, so PoP was super fun. I do agree with it being optional though, it would be terrifying for the casuals if it wasn't