Reusing Protagonists and Rivals

So by the title,why didn't they reuse the rivals as professors instead of coming up with new ones?Aren't the games set years apart so...I'd love to see Red become a professor in the Gen 8 games?
This one sounds weird but why can't we transfer over our old characters into newer games?Like how Ash does it. We'll have to leave back our old Pokémon and start fresh but keeping our old gym badges and clothing?In turn showing a league champion we've conquered previous leagues we get some kind of reward...?That'll be nice?I know the 3DS probably wasn't powerful enough to do such but with the switch it opens the possibility of it happening.

being able to transfer our character to the next game would be cool as fuck

That would be a cool feature to introduce into future games, especially if Game Freak continues to make Pokemon more plot-oriented (i.e. Pokemon games tie directly into each other canonically).

Now the question begs to be asked whether your avatar would be a Mii-like character, or would Game Freak continue to utilize their silent protagonist formula? Perhaps GF can further break tradition, and make your character have characterization (like a JRPG)

I can see both pros and cons to this.

The pros here is that your character is essentially you; it creates more immersion into the game if, instead of being forgotten about everytime you start a new journey (game, in this example), you'd be able to just transfer over as if you were just starting completely fresh. It definitey helps in that aspect, but there's a trickier side to this, I think. That is: what happens to the current main protagonists of the region?

Idk, I feel like it would just get messy because people's preferences are so varied on which protagonists they'd prefer and want to transfer over from game to game and I feel like each "region" wouldn't have its own "protagonist" so to speak because it'd be hte same protagonist that came from the same region.

It'd probably be really messy in execution. :s