https://techcrunch.com/2021/01/08/why-twitter-banned-president-trump/

Twitter permanently banned the U.S. president Friday, taking a dramatic step to limit Trump’s ability to communicate with his followers. That decision, made in light of his encouragement for Wednesday’s violent invasion of the U.S. Capitol, might seem sudden for anyone not particularly familiar with his Twitter presence.

In reality, Twitter gave Trump many, many second chances over his four years as president, keeping him on the platform due to the company’s belief that speech by world leaders is in the public interest, even if it breaks the rules.