The CEO of CloudFlare famously said that the reason he decided to deplatform Daily Stormer (after previously saying he would not deplatform them) was because one morning he woke up in a bad mood and decided to kick them off the internet. Literally all it took was one CEO waking up on the wrong side of the bed one morning. It seems entirely inaccurate to say that Dorsey or Bezos couldn't make a decision unilaterally like that if they really wanted.

I'm not sure about Twitter, but Bezos is the majority shareholder at Amazon and if he really wanted to, could make the decision to ban anyone he wants and nobody would legally be able to stop him, will of the employees/shareholders/public be damned.