Are they?
Fortnite has hardly any cohesive artstyle.
Do you really want the artistic aesthetic of Overwatch to become a slave to the highest bidder?
Oh, I’m pushing a Ferrari across this map while it shouts slogans at me and talks about how fast it can go, the robot on push is now a Transformer, Numbani is now Black Panther and any canon, lore or artistic style has been stripped out and replaced with a glorified advertisment for Disney.
Crossovers harm those who want to enjoy the base product and strip out any artistic vision that was once there. Blizzard are greedy enough with this game, we don’t need to give them more reasons to tear out the innards of Overwatch’s artstyle when the team have done so many great things the past year in this department.
Please stay away from Halo, we have enough issues with Microsoft shoving clashing armor sets into a military-scifi setting.