Keita wasn’t popular in Japan.
Based on J Twitter/forums, Japanese audience picks were Geunwook and Mathew.
Seems like Keita was mostly their “Japanese member filler pick”. Most of his votes were from international fans (like Jay). I’m sad he didn’t make it but not surprised he didn’t debut since he didn’t have much Korean/Japanese support.
Mnet/Produce groups are pretty popular in Japan. Having Japanese members helps but i don’t think it’ll negatively affect them. There’s been Kpop groups(BTS, Kara, SNSD, TVXQ, Blackpink) that have been successful in Japan without any Japanese member.