Little late but some reasons were given for Sam being ousted.
Non-paywall
Sustkever is said to have offered two explanations he purportedly received from the board, according to one of the people familiar. One explanation was that Altman was said to have given two people at OpenAI the same project.
The other was that Altman allegedly gave two board members different opinions about a member of personnel. An OpenAI spokesperson did not respond to requests for comment.
Interesting to note that Sustkever is disassociating himself from the board.
Both of these reasons in my opinion are complete crap.