According to Dorsey, they didn't want to block Trump, they caved in to advertiser requests.

"But [the Trump ban] was right for the business, because if we didn’t act on it, we probably would have lost all our advertisers, which would affect the business and stock price. But it was wrong for the world and the internet, given the fact that we could do it in the first place. No one should be able to do that."

https://www.piratewires.com/p/interview-with-jack-dorsey-mik...