This topic has been covered quite a bit in past posts. However, I opine that a major reason for Mike excluding Tom from certain intimate family conversations was Mike's belief that Tom was, in part, responsible for Sonny's death because the families faked him out and that he just was not a wartime Consigliere. That he was a fine lawyer with a fine mind in that regard was great, but a Mafia Don needs someone with cunning which Genco had, but Tom lacked.