Yeah, because that's something that should require buying separate games instead of a simple difficulty toggle like every other game ever made...
I understand your point and agree with it. At the same time, "difficulty toggles" don't always legitimately up the difficulty. Simply making the numbers bigger and requiring more grinding, to me, isn't a satisfying difficulty change. I'd prefer completely changing trainer layouts and teams, further spaced out Pokecenters and rest stops, altered routes that make previously optional paths now demanded for you to get to the next town, etc.
All of this can absolutely be put in one game, but they've gotten away with selling two of the same product since 1996. I'm just saying that giving players the option at purchase of an easy or hard route with significant differences would actually make the split games thing have a purpose for once.
I legitimately don't know how selling two-to-four of every Pokemon game doesn't get, like, any backlash at all. If EA tried to sell "Dragon Age: Exalted March" and "Dragon Age: Tevinter Imperium" as two sides of the same game the internet would be torn asunder over it.