beta
I think the possible idea as to why the OG wants his body back is mainly due to denial and also like you said, jealousy. Of course it would be easier to reincarnate, but I’m guessing OG feels a sort of attachment to his body and denies the fact that suddenly our MC can do what OG can’t. It’s shown that OG is very stuck up, stubborn, and also selfish in a way.
And adding on to a somewhat toxic family environment and struggling relationship he had with his teammates due to his personality just made it all the worse. So when he sees that MC is flawlessly getting through, especially as being HIM, it’s a huge blow to his ego/character and personal self. It’s like a loss of worth to him, and all he sees is the massive L rather than how to change.