In kayfabe, I don't know, she's focusing on her new life as a tag team wrestler.
Out of kayfabe, which is what matters here, they don't want Asuka in that spot. They never treated her like a true champion after her and Becky were done with each other, she faded away into irrelevance. She only ever beat Becky to put doubt in fans minds that she might not win the Rumble.
And now they've got Becky as their top woman. Charlotte's still in the mix. And they want to push Lacey. And with Asuka they're keeping her busy with Kairi to give her something to do.
No grand explanation but again, Asuka got her reign because Becky had to lose, she didn't do anything with it once Becky was out of the picture. And now that Becky has her belts, they've got Asuka down the card doing something else.
That was more of a Charlotte/Becky feud with Asuka thrown in the middle. Throughout late December to early January, Asuka only had a sinlge one on one segment with Becky. There's also that pre-RR brawl and the-post TLC SDL but, as I said, those were more like the usual Charlotte vs Becky segments, only with her as a special guest to prevent the fans from complaining about Charlotte getting TV time nonstop.
And let's face it, the RR loss was to make Charlotte Becky's kayfabe equal. By having Becky be unable to defeat Asuka but then have Charlotte do that on an often basis without sweating, you are basically saying that Charlotte can do what Becky can't. And the best part is, this way they don't need to have Flair pin Lynch or make her submit, so they also avoid angering the Becky fans.
I'll say it again: how many times has Becky defeated Charlotte clean since tuirning face again? Zero. Those two clean loses during early Autumn were done to get Flair sympathy from the fans, but since they still favoured Becky over her, they said screw it and went back to hteir usual booking where Becky cannot get the better of Charlotte unless it is through DQ or similar tricks.
she can't promo....Becky would have to carry the whole feud
Charlotte can speak english and Becky had to carry the whole feud by herself still the same so...
Anyway, it's more than the promo issue. vince refused to give her a mouthpiece all throughout 2018 because he thought that way he could avoid having to give her the belt (and even then, he ultimately failed at this), and now that she has a mouthpiece, they keep her in the tag team. but then again, Paige has beeen placed there to be Kairi's manager, not Asuka's double standard much, Vince?)