>>6504299People aren't talking about how "unprofessional" this is because its Brock Lesnar. Unlike Sasha and Naomi, people actually like him.
More to the speculating though, I see three scenarios:
1. This is a work. Manufacture some extra controversy to get more eyes on the product and its new direction.
2. Brock was pissed about Vince leaving and doesn't want to answer to Stephanie and Tony Khan. Vince probably ended up calling Brock and convincing him to come back and hang around until the end of Summerslam.
3. Brock used Vince leaving to mercenary more money out of WWE.
All scenarios seem plausible.