Why is it gen 5 of all gens that was the most divisive? Later gens had more vocal minority hatred but they still sold better and were liked by the majority of casual players. Half of the people I meet do not like gen 5.
I do not believe it is because of old pokemon being missing, because the dex cull of gen 8 didn't mean shit, so what is it exactly that turned people off? Thew new designs being "ugly"? The more story focused campaign?

This generation was designed in mind with trying to win people who had fallen off the franchise back, but it seemed to have the opposite effect. I think Pokemon fans are not ready for big changes.