why is the Pokemon replay factor so bad?

In conventional RPGs, the famous "plus" mode is very common where after finishing the main story you can start the game over with everything you achieved in the first gameplay. To have an experience similar to this just by buying the alternative version and making trades, which is not the same thing, since there is the "obedience" system of the Pokemon levels.

I am not saying that the obedience system is bad, in fact for me it is cool and important for the player not to break a game that is already easy in itself. I'm also not saying that extras like Battle Tower, Battle Frontier and co are bad but I mean that everything could be better.

I think that if Game Freak hadn’t invested in useless and niche things like Contest and added a "replay" mode plus a system to lower pokemon levels, it would be perfect. Just imagine you restart the game using your favorite legendary level 5 in which you battled and captured cathartically in another game in the franchise. But thinking a little and knowing Game Freak I venture to say that the intention is really that, make the player sick soon to buy the next game