Its a question of what is manipulation. The reason this all started was because hedge funds shorted over 100% of the available shares which meant that if enough people bought the shares and didn't sell then they had them over a barrel. Thats not manipulation, thats taking advantage of market position. Shorting over 100% of a stock however... that is guaranteed to tank the price of a company. Basically labels it as a sinking ship.
Again, is that illegal manipulation, I have no idea but I'm pretty sure that stopping people from buying and only allowing selling under the guise of "protecting peoples money" is very dodgy and other people have pointed out, exchanges like RH have been quite happy to let them lose huge amounts on other shares. Difference is that their sugar daddies are on the line this time.