1st, of all there's time control. 2nd, the player has the right to keep trying. It doesn't hurt the losing side to move his king around to random squares, but that isn't the main issue. The main issue is when people take advantage of the rule to escape inevitable mates, such as this example from the blitz championship:
Black claims Nb8 was move 50, but he still is mated next move. In this case, the game will end, next move, so there is no reason to claim 50 move rule. The 50 move is rule is to stop obviously drawn games from continuing, not to give draws to losers. The arbiters granted white the win, and rightly so.
There are at most a few hundred examples of games where someone will win in over 50 moves but a million more examples of games where its impossible to win. What would you do then?
It doesn't matter how realistic or rare the endgames/positions are, the rules of the game has to take ALL possibilities into account.