Token Curated Registry was a very popular idea in crypto long time ago. like pre-2020

what happened to it? any successful examples? any reasons why there aren't any successful examples?

still a powerful idea.
didnt work cause it focussed on hyperfinancialization first, without utility (cant blame, it was 2018 era). people just created registries for the sake of it.
I think it will resurface once TCRs get both a distribution and utility surface. 
imo twitter’s community notes is a tangential example of communities coming together to curate stuff.