Both of those require a player to claim the draw. There is no reason within the rules of the game for why it could not be infinite in the # of moves. The rule has also at times been restricted only to tournament play.

Also, if chess was "solved" and board states determined "winnable" after significantly more moves, the rules might very well change to extend that limit.

Something along those lines has happened before: When a combination of pieces have been shown to be "winnable" but might exceed the 50 move rule, exceptions have been made to the rule to allow more time to develop the win. At some point though, the rules went back to 50, but still with conditions about pawn moves, pieces taken, etc.

The history is interesting: 50 was originally chosen (or maybe just compromised on) because players felt than all winnable games could be won in 50 moves or under.