You do realize re-buying old games is optional, you don't actually have too. You can stick with new content like Pokemon Snap 2, Bravely Default 2, etc.
It isn't like the Switch doesn't have original content. Mario Odyssey, Pokemon S/S, Luigi's Mansion 3, Fire Emblem 3 Houses, Octopath Traveler, Astral Chain, Link's Awakening, Mario vs Rabbis, Origami King, Trials of Mana, Xenoblade Chronicles 2, Splatoon 2, .
If you only own 3 games and yourswitch is "collecting dust" since launch, too each their own. But there are some quality games you simply haven't picked up.
And we have Monster Hunter Rise coming out shortly.
Sure, there are games. But, they have definitely relied heavily on Mario universe retreads this gen, and those are the games I buy Ninty systems for. I don't think there's any reasonable argument to be made that the number of new entries in their big franchises has been low. We're at four years in now, and we have relatively few completely new games in the Mario universe.