Is high-level competitive Overwatch play really popular enough to justify this? It doesn't even look fun to watch for the average person.
So a few years back, Activision noticed that they had zero capability to launch new IPs outside of Blizzard, and bought MLG in an attempt to turn eSports into an NFL like business. Part of this was hiring the former president of the NFL and I think a former CEO of ESPN.
The idea was to do this with Call of Duty, but they realized no one cared about Call of Duty, so they eventually transitioned the idea into Blizzard with Overwatch even though it was supposed to be a new way for the Activision branch to generate revenue.
This is similarly why they started a Film and TV division shortly after focused on Skylanders TV shows and Call of Duty movies, though they reserved the right to move that over to Blizzard's IPs if it failed in the Activision branch.
Eventually they realized both of these were hard, and just bought King to try and solve their issue of Activision being unable to support more than two game franchises, so they could at least grow with two of their branches (Blizzard and King).
But basically, this is the implementation of an idea that was meant for an entirely different product due to creative bankruptcy on the Activision half, so it was kind of just forced on there, and we're seeing the results of this with the astronomically slow uptake of franchisees.