For wives to go to bachelor parties with their husbands?

My BIL is getting married soon and his best man set up a bachelor party, I assumed it was only going to be the groomsmen, groom, and my FIL. (My husband was supposed to be the best man but that's a different story all together). Well the best man is bringing his wife and didn't extend the invitation to any of the other wives including my MIL. I didn't want to go since I do enjoy my time alone I just thought it was odd that only HIS wife is allowed to go. He wasn't even going to tell my BIL until they were already on their way to the hotel but apparently it slipped out mid conversation.