My guess is they're having trouble with the kenki cost of Kaiten in the opener and burst. Maybe they want to add more kenki skills but can't find the room because we're sort of locked into using Kaiten on iaijutsu. Its value is hard to beat.

They seem to be having problems in general with finding space for all the new shiny skills in openers, hence why they keep removing GCDs and oGCDs from NIN and making their raid wide buff 20 seconds long. It's ultimately a problem of their own making because they decided everything has to revolve around 2 minute burst windows.

We generate 135 kenki in the opener, and Kaiten eats up 80 of it. This may be why they reduced the kenki cost of Senei/Guren from 50 to 25, because we now have to throw in extra Kaiten to buff Ogi Namikiri and a 2nd Midare. There's technically 30 kenki still available in the opener, but some of that may fall out of buffs depending on timing.

Even if this is the case, there are still better solutions than outright removing Kaiten, especially now when it's not a problem.
  • Remove Senei's kenki cost completely. It's not like we'll ever not have the kenki for it since it lines up with Ikishoten. This saves 25 kenki in the opener
  • Reduce the kenki cost of Kaiten to 10 and make it buff iaijutsu only. Yeah, it'll further trivialize kenki management but if they want to give us a new shiny to make up for it, I'll take it. This will save 40 kenki in the opener
  • Have Meikyo Shisui generate an additional 5 kenki per GCD. This adds 30 kenki to the opener