GMs aren't privvy to SPG agreements with the events/promotions that they've done with other TTRPGs like Pathfinder, Pirateborg, etc (the list really does go on!). Of course I'm curious, but I'd be very surprised if WotC was getting a cut... I can't imagine it'd be a drop in WotC's bucket financially; SPG gets 10% of a GM's per-session fee.
But if it gets more folks hooked up to DnDB,
that's worthwhile to WotC.
You might not believe the sorts of comments and messages I've gotten about pay to play! I started at $25/session and am currently at $39 per. It took a lot of getting over myself and the taboo we grew up with around paying to play TTRPGs. If it weren't for my wife pushing me, I wouldn't have gone from being a law clerk to a pro GM
There can be a big difference between an AL session at a FLGS, versus the experience a higher-cost GM might offer.
P.S. I tried doing a biweekly game to both give myself a break, and because some players are willing to pay my prices-per-session but can't budget to do so weekly... it turns out none of us loved it- and I actively
disliked it due to a lack of momentum.
Some of my players play in 2-3 of my games per week
The best is when we get multiple sessions of the same game in per week- for the players it's like being a kid again, playing so much and
really getting into the game. For me, the momentum is fantastic for the creative juices.