It does say "unauthorized", so I assume it should still be possible to get an official license to make a third party controller, though we'll have to see if that's actually going to be the case.
It doesn't have to be profitable for them. It can just exist, be the only option, and prevent others from making a competitive or superior product, forcing others out of the business.
It would be a shame if someone with a physical disability needed to find a different accessible controller for each platform they play on because each one only supports first-party controllers though.
I don't have a disability serious enough to need adaptive controllers like this, but I do have RSI, and when I find peripherals that I can use with minimal pain I stick to them. I have to imagine many with more serious disabilities would feel similarly.
This might be a sad day. Ben Heck has been making accessibility controllers for as long as I've been on the internet and I know the last few videos he's done on those have been based off a third party controller.