I mean, they could've bought it if they really wanted it badly enough.
I think you forget this is Japan not the UK the poster formerly know as Tyrion. WWE can steamroll the UK scene but Japan is a different story altogether. WWE isn't even that popular in Japan compared to the likes of NJPW or NOAH these are facts. I think they even do well to draw in small crowds to these NXT Japan tapings. As it's know wrestling fan's in Japan are loyal to their companies.
I can see them maybe cherry picking Joshi talent, but rumors going around that Stardom (former home of Io and Kairi and homebase of Riho and Bea from AEW and a lot of non Japanese talent in NXT and NXT uk even the main roster worked there) is going to strike up partnership with NJPW. So that's the biggest Joshi company out of their hands. Even if it's not Stardom, NJPW are going to do with something with Joshi wrestling. So expect them to go out and pick the best talent they can get.
The rumors are Meiko Satomura is going to be head trainer for NXT Japan. Also that means Sendai Girls is on NXT Japan books, and also the rumors that it be Big Japan Wrestling too.
If you don't have NJPW (which WWE were never going to get), NOAH (they struck a deal with Impact) and All Japan Wrestling. Also looking likely that biggest Joshi company in Japan Stardom not jumping aboard. I don't see NXT Japan doing any damage to Japanese scene like they did to UK one.
No way do I see Kairi, Asuka,Io or Nakamura going back full time, they left their companies in Japan for a reason lol. And won't go back to wrestle in front of 200 people or slightly more. What's the point of some top talent leaving Japan just to go back again to work with a company that no one but a cult will watch, like what's happened with NXT UK.