3PP are nothing to WotC. All of them together are a rounding error on the D&D books, let alone WotC's total revenue.
Unless they're doing something that hurts D&D, they're not worth thinking about.
Uh, if they are a rounding error, then why does WotC care? Given that you completely misrepresented the whole deal with cancellations, I can't say I have much faith in your pronouncements on the sales of Wizards and 3PPs.
But more to the point, giving people more chances to find an audience with other games sounds like something that is way better for the industry than simply having to force everything into the 5E market.
It's exploding because of Dungeons & Dragons. If D&D goes away or gets hurt by this, it's not going to keep growing at the same rate. Because a common well known entry point makes it easy to find games. And once you have a group, it's easier to get them to try other games.
It's exploding because people are playing RPGs. The idea that Dungeons and Dragons as a brand drove this misses that it was simply people introducing people to the concept of roleplaying via things like Critical Role or Stranger Things. There is nothing intrinsic in D&D right now that is really driving this explosion other than its name.
The last time D&D went away (4e) the entire industry shrank and contracted.
Did it? Are you sure about that? Or are you just saying it?
And what do you think is going to happen if Wizards can destroy any 3PPs or VTTs they want because of their new policies? Might be good for WotC, but it'll be to the detriment of anyone outside of them.