The same reason why any kid with low self-esteem gets absorbed into video games. They can be The Rock in them, they can be the Heisman winning quarterback in them. In only a few years of full time counseling, I had several therapy clients who were late teen/young adult males who were absorbed in video games because it was the only place they felt like they mattered.

Now imagine if those video games were as all-encompassing as the Jumanji game. Run away from reality and be that dude? I can see the appeal.