The foundation probably thinks Gox may not end well, and threw him out early, before the foundation takes any damages
Probably? It makes a huge speculation difference!
There are two mainstream guesses:
1. MtGox is in grave danger of bankrupcy, and they are struggling to buy coins from panic sellers to redeem themself. Evinced by lack of any positive news when they had plenty of opportunity to calm investors - and refusal to answer if they still have client's coins - once by Roger and another time by WSJ.
2. Mark K. is not a personage for his position. He is confused and naïve, and chose to evade the situation.
(it could be 1+2 both)
The foundation has little reputation, because in this crisis they did nothing to protect bitcoin as they vowed to. The media coverage and lose of public confidence is perhaps the worst experience in bitcoin history and they acted nothing more than pointing out that it's MtGox's problem - that tells a childish leader from a mature leader.
Consider that now is the worst moment to quit from the foundation. If Mark K. is doing it, either he needs more bad news to keep GoxCoin down for him to purchase to redeem, or he has extremely bad judgement of timing. The former possibility is getting less and less likely as he got plenty opportunity for cheap coins already. So the wager is on the second, that he is oblivious and naïve - in which case quitting the foundation is a piece of good news, because a naïve leader with insolvent situation should be in of the 5 stages of failure acceptance; while a naïve leader with solvent situation has the heart to wrestle bitcoin foundation reputation with his.
So:
Bitcoin foundation kicked MtGox out = no influnce to speculators, the foundation isn't important.
MtGox decided to quit the foundation = raise the wager on MtGox solvency.
P.S. I looked up the news, Karl asked to quit. Bitcoin foundation may feel happy that they got rid of a problem, but their incompetence to protect bitcoin is evinced in this story, they are already doomed.