Shorting is betting that a stock will decrease by borrowing the stock from someone else, immediately selling it, then buying back the stock at a lower price to sell back to the entity you borrowed it from. WSB realized that there were a HUGE number of shorts of Gamestop, AMC, Nokia, etc.. More shorts than actual stocks available to trade. The thing is, because when you short, you're forced to buy the stock back, so any increase in price is more and more loss.

Some hedge funds had massive shorting positions in Gamestop. At some point, they'll have to buy the stock back to return it to the original lender. WSB, by encouraging purchases of the stock, increased the demand, which in turn, increased the price. The hedge funds saw that the prices are going up, so they themselves scramble to buy back as much stock as possible at as low of a price of possible. This, in turn, drives demand for the stock up even MORE, skyrocketing the stock price in a cycle.

The thing is, when this started to happen, the hedge funds bought even MORE shorts of companies like Gamestop. That's because the price has already spiked, so it's almost guaranteed to decrease again once all short positions have been returned to the original lender.

Here's where the issue is: many of these hedge funds are investors of Robinhood and other trading apps. They very likely directed Robinhood, etc., to prohibit investors (including everyone at Wall Street Bets) from purchasing Gamestop stock. Thereby decreasing the demand for Gamestop stock again (to essentially 0), lowering the price and allowing the hedge funds to make some of their profit back when they cash in on the NEW short positions they bought at Gamestop's price peak.