Let's not overstate this, the official POTUS account is not banned and it's not going to be banned (although it might get censored), just citizen Trump's.Trump getting banned is the scariest part, though. I mean, you have removed the president of the United States himself from a communication channel that has no alternatives at the moment without as much as an order from the Nowhereville county court (which lacking regulation makes impossible to seek, one needs to add).
There was a good reason to do this which was publicly argued by the tech companies - they are rightly careful to be transparent with their reasons.
Of course they could abuse their powers in the future, but this was not it and they will get serious flak for that.
Even now Twitter got a stock price hit for deplatforming Trump, so it's not in their interest to go further down this road.