Fighting Joey Optional

I recently found out from the awesome Johto guide that after you take the time to beat the gyms, team rocket and finally the elite four that you must fight Joey with a lvl 80 rattata in your party in order to move on to hoenn.

I don't understand why this is an absolute part of the game. It seems like this should be an optional or side quest instead. It takes a really long time grinding to get any Pokémon to lvl 80 and if you don't have an everstone (like me) , you have to not accidentally hit yes every level it goes up. Why must you fight him besides moving to the next region, what's the point? Does he give you something you absolutely need that's crucial, money, better exp? For any player that doesn't ever look at the guides, they would never know about this info and thus be stuck, confused and maybe get frustrated and quit. Which would mean they would put all hours of pro down the drain because they can't get to the next region or don't want to waste more time and energy into one rattata. I thought pro was supposed to be the game where you could potentially go to every region by beating the pro story and the gyms and elite. Not wasting energy on rattata when it doesn't really benefit you except to move on. I'm not trying to be angry or rude (please don't take it that way) about this at all BTW, I am just trying to understand why this is absolutely important to do.

Please let's make this optional, we already have to do a lot of time and work just to get past the elite four and your Pokémon get locked anyway when you go to the next region.

Thank you ^_^