For the sporty kei stuff, I have no idea other than maybe some official got a complaint or concern from a kei car involved accident and then they overreacted out of fear. There's definitely some shenanigans afoot with lawmakers trying to ignore the 25yr ruling.

Part of me wonders if there's not weird racism involved somehow. My ancient VW is waaaaay less safe than a '90s Kei car, yet it faces no issues. That's not even getting into classics whose collision mitigation tech is mostly "well, the steering rack will at least impale you pretty quickly."