Why mumblecore didn´t get famous?

This is an honest question.

And why nothing else gets famous, like grunge did, or britpop?
Actually I can´t tell something(or someone) is famous unless my mother knows it, I don´t watch much television nor listen to the radio, so when my mom says "it´s a shame she´s a drug addict, she sings so well" about Amy Winehouse, I know she´s famous

In my teenage years mainstream was cooler than now.