these are often gonna be something that you get after deciding not to get provinces, for the time being.
pros vs. provinces:
-they help you before the game is over
-$52 vs. $64, scaled conveniently
-comparable vp—having all castles is minimum 45, and grand castle can potentially push it over 48
-game doesn't end with the pile; good because you have built a bit more by virtue of having castles
cons vs. provinces:
-a couple extra junk cards—silver, duchy (or estates), maybe gold lmao
-humble and king's castle have huge bites taken out of them if the opponent denies a few castles, and it is very often easy and convenient to do that, especially via small castle milling
-pathfinding on castles, draw & discard pile empty; use king's court on small castle
so maybe they don't want to compete with provinces, i dunno. they do all do different things.
-is it at all possible that someone can roll over the castles in entirety and take all of them?
-or does no one ever even want to be the first one to pick up humble castle?
-what determines a game where these are appealing or unappealing? ability to draw/play a bunch of victory cards? +buys?