Actors who mostly disappear after their shows end, despite phenomenal performances?

I mostly notice this with all the side characters on HBO series, but I hate how many times an actor just blows me away and then mostly disappears after, only showing up occasionally in bit parts.

One of the most painful ones for me was Janel Maloney, who played Donna on West Wing. Only to show up on The Leftovers as an invalid with no lines.

Also most of the cast of Deadwood.