>>49517617Various things could have contributed. For Stantler, styles could have become an entirely lost art in modern Pokemon battles, combined with less older Stantler/Wyrdeer teaching it to their young, thus rendering the evolution inaccessible. The specific plants needed for the organic materials in the Peat Block that lets Ursaring evolve could've gone extinct in area in the period from then to now. Johtonian Sneasel and Qwilfish were introduced and outcompeted Hisuian ones (this kind of thing happens a whole fucking lot irl), White Stripe Basculin either wholesale migrated or went extinct in the region, the environment dried out so that Goomy couldn't sustain a population, let alone ones with material-costly shells like Sligoo and Goodra (this reasoning is close to why Slugs lack shells despite evolving from a shelled creature like Snails did), Black Augurites had their deposits depleted making Kleavor effectively extinct, etc. etc.
