>>23315163
Except Kuuga did do that explanation, Zajio points out the metal in the meteor is the reason their bodies are all fucked up and Kuuga's belt is made of the same metal. This even came to a climax where he fought a beetle-themed Grongi with the exact same form changes. It's not that there needs to be a detailed explanation, it's that acknowledgement of factors and trying to say anything about it at all helps the world be actually interesting.