I honestly went and read those release notes just to check if they're using this transition as an excuse to make the game less cross platform.
Java edition has never been playable on anything other than Windows, Mac, and Linux, porting an SDL version onto any of those is extremely easy.
Getting everyone on one platform is a much better model for Microsoft than trying to resell you a copy on each device.
That IS cross platform. One, two, three platforms. Count them.