They don't help underrated pokemon, they replace them. Sometimes, it fails to do even that by making a shittier version of the original. And it's a slap in the face when only the regional variant gets a cross-evo, making the original even more worthless by comparison. Not to mention that it's just lazy padding, because why make a new species with new interesting ideas when you can slap those ideas onto the same old pokemon and resell them over and over again, followed with immense praise?
So, why do people want more of this, even more so with fan favorite pokemon?