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At the risk of sounding like Yawnfag, you can trace the issue to gen 5.
BW was the first time Pokemon seriously tried out the multiple rivals concept (Wally wasn't really a rival and was barely present). Cheren was the traditional competitive rival who thought too highly of himself and grows frustrated over not being able to beat you, while Bianca was the real progenitor of the friendly rival trend. She was a good natured, friendly girl who didn't know if she actually wanted to be a battler or not, eventually deciding to become a lab assistant to the Professor. It would seem that the majority of players came away from BW preferring Bianca to Cheren, after all she was a nice girl with a fat ass and a decent character arc, but Gamefreak took this to mean that players preferred the friendly rival over the asshole rival. The general apathy to Hugh in B2W2 likely reinforced this assumption.
As such, the next 3 generation starred Bianca clones. Friendly, good natured, and uncertain children who took the starter weak to yours. Hop even randomly decides to be a lab assistant despite nothing in the game pointing towards this being something he might want.
Thankfully, gen 9, despite all it's problems, took a step away from carbon copying Bianca again
