Collusion in these markets are always unstable and short lived because the collusion itself creates the incentive for individuals in the group to "cheat". The "success" or the rise in GME prices also makes it attractive for people on Reddit to profit take. If you are a Redditor that is holding GME you have incentive to tell others or to buy while you sell.

The success or rise in price also gives an incentive for hedge funds to re-short and the re-short becomes more difficult to squeeze than the original short. Hedge funds are already resetting the their shorts at the high 300s price. If you are gonna squeeze those hedge funds you would need to drive GME even higher. The $300+ stock prices means that it is difficult for you to buy enough shares to do that.

The people who bought GME at over 300 are now the ones that really get squeezed because they are going up against short sellers and they are also being squeezed by other Redditors who are panic selling.