Windows 11 is getting out of hand with its push for advertisments, frankly - remember the recent full-screen pop-up to persuade users to install Edge or other Microsoft services? Then another advertisment was placed in the Start menu, and now Microsoft has finally worn my temper thin - with a new Game Pass ad coming to the Settings app.
This will likely arrive in the July update for Windows 11, or at least it’s almost certain to do so. It was present in the latest preview update Microsoft just released for the OS (and quickly paused due to a bug, but that’s another story). It’s also worth noting that the ad has been present in earlier test versions of Windows 11.
JXL is new (like 2 years old), webp is older (> 10 years). Adding support for a thing takes time and resources, which is lower priority when there are good-enough formats already supported.
At least that’s my perspective as someone who interacts with product owners (i.e. the type of people deciding what features get prioritized).