The 50 move rule is a rule of chess so it must be considered.

The 3 repetition rule is an opportunity for one of the players to declare a draw, but games can continue beyond that. The mandatory draw rule is 5 repetitions. In any case, the 50 move rule is far more limiting as to the number of moves in a game, since repetitions are necessarily neither pawn moves nor captures (the whole point of the 50 move rule being limited to those is that they are irreversible).