If there are locked rooms, shouldn't there be somewhere in the whole run a matching key? Sometimes I even find multiple locked rooms within one seed and there isn't a single key to be found even after exploring 100% of the run enviroment. Ore are keys somehow hidden? I don't get it.

There have been a few changes with this, iirc the latest thing was to have no useless keys, but there can be extra doors to give the player choices.

Well it feels like after one of the recent updates, i keep seing locked doors, but I havent seen a single key since then. So any locked door basically means one less reward for that seed.