I'd want to make sure that there is no way to game the system (by playing some games more quickly than others). Probably sufficient for this purpose would be to have a rule that there are never more games going on than are needed for the player in the lead to win.
I can think of two other possible reasons, neither of which seems compelling in my opinion:
1. Some people don't like so many games to happen at once. Of course, these people probably aren't the same people who play 50-point matches anyway… For this reason, I would suggest 5 or 10 as the limit, not 50. However, one way to avoid this altogether would be to make this an option, such as “propose starting another game” which could be accepted to declined.
2. It could be that someone would play differently based on the overall match score.
