Jeff Kaplan explains why here…
Overwatch League is the premier esports league of Overwatch and the PC platform is the most optimized way to play Overwatch. Those interested in climbing the path to pro will transition to the PC platform. PCs are easily customizable too. In fact, Overwatch League itself is a custom Local Area Network setup where each player’s PC is part of a greater server infrastructure (in otherwords their PC isn’t even in the same room they play in).
This may sound cruel, but its like trying to bring a street-legal Honda Civic to a NASCAR race. PC is a far better way to play Overwatch and the BattleNet platform is Blizzard’s platform so it is easy to execute events on PC.
There are third-party console tournaments including the Console Gaming League:
Gotta switch to PC if you want to make a living in a professional esport. It can’t just be given to you.
I will say Consoles are great for the casual gamer, there are console exclusive esports of course like Smash, Call of Duty, and Street Fighter, but those games are designed primary for Console, Overwatch is primarily designed for PC, but gives the opportunity for console players to enjoy the game. Every single in-game item can be earned on console, consoles get the same seasonal events and benefits as the overall PC community. While PC is preferred for esports for very good reasons. Consoles are a great no-hassle option for anyone who are not focused on building a Esports career.