Because after match is ended by system because run out of match time the positions are decided by who has the most time left. There can be situation when the player who is leading the game and would definitely win it, would be ruled-out of tournament because he got less time left than others. I do understand the leader kicking out than the slacker in order to have a chance to stand in tournament.
The madness starts when the player who would definitely lose the game is kicking the slacker, and whats more - I seen situations where game was already decided, and would be finished on time (if not reaching the deadline on purpose by one of two players who still haven't finished the game), so 6 players, 3 advance, 4 are already finished the game so the winners are decided, 2 still playing and they have 3 options - finish the game on time, not finish on time on purpose and the game might be ended then by system (this might also happen not on purpose), and last option is that one of the player who would lost is kicking another who would lost. Both last options are not cool.
Culture and dignity of tournament players would help here the most :/