Io and Kairi speak for Io and Kairi. Plenty of Japanese wrestlers for some reason or another see WWE as the place to be. Io and Kairi's motivations for leaving are clear but also not universal. Kairi has been outspoken about wanting to appeal to kids with wrestling and that is the opposite of WWE's demo and the opposite of her current booking. As for Io general discontent with living in Florida and dating Evil will do that. I think Io might go back to Japan because Bushi Road is opening the piggy bank but Kenny has been outspoken that there is no talent he wants to land more than Kairi. Either WWE offers her so much money it would be foolish to decline or Kenny offers a platform to do what she has wanted to do with some of AEW's new money and she fills the Kylie Rae shaped hole at the top of the card.
Io has made it pretty clear her end goal in WWE is to make money and get exposure
worldwide. Something that Bushiroad cannot provide her with. At least compared to WWE. Plus she already had a ton of exposure in Japan anyways, appearing on various TV shows, and various publications. She also sorta put STARDOM creative on blast a couple of months ago in an interview with Pro Wrestle Magazine (JP publication), because she's had her current NXT character in mind for a very long time, but they wouldn't let her do it in STARDOM because she made them too much money as the "ace" of the company. And that was before Bushiroad forced out Kagetsu and Hazuki, the two people she personally handpicked to lead the locker room.
As for being engaged to EVIL, Dave is just speculating that she's unhappy, but she's also posted on her blog in both November and December emphasizing that she's pretty happy working for WWE right now, and has settled into life without any issues in Orlando.
Kairi is in a weird spot booking wise, but lots of adults still bring their kids to house shows and TV tapings. Those are the people she wants to appeal to. That younger demographic. She's not trying to appeal to the 18+ demo. But she's probably going to get a huge sack of cash to stick around in WWE considering Gallows and Anderson are getting a combined total of $1.5m. And with Kenny letting it slip that she is priority #1 for AEW's Women's Division, that will probably spook WWE a bit more as well.
As for her plugging the Japan tour, she sent out a tweet saying she will definitely be there to wrestle in front of her home country. So no, I don't think her contract is up soon like Dave seemed to speculate. Casey hinted at it like three/four months ago as well, saying people needed to stop wasting time speculating on the status of Kairi's contract and instead focus on contracts that are actually up soon.