Because the implementation was a shitshow. There was no verification that uploaders of popular mods were the actual mod creators, anybody could rush to be the first to upload something.

With Bethesda taking a cut of sales, and the fact that the community wasn’t fond of Bethesda encouraging monetisation of content and mods that should’ve been part of the base game(s) it’s no surprise it flopped.

I would like to see them at least donating more to projects that actively bring their games to playable states.