They haven't really said anything about why it was, and according to business insider[0] (the only reporting that I've seen that says anything concrete) the reasons given were:
> One explanation was that Altman was said to have given two people at OpenAI the same project.
> The other was that Altman was said to have given two board members different opinions about a member of personnel.
Firing the CEO of a company and only being able to articulate two (in my opinion) weak examples of why, and causing >95% of your employees to say they will quit unless you resign does not seem responsible.
If they can articulate reasons why it was necessary, sure, but we haven't seen that yet.
[0] https://www.businessinsider.com/openais-employees-given-expl...
When 95% of your staff threatens to resign and says "you have made a mistake", that's when it's time to say "no, the very good reasons we did it are this". That didn't happen.