And the earth opened its mouth and swallowed them up, with their households and all the people who belonged to Korah and all their goods.
Numbers 16:32 ESV

Evidently some of Korah's sons did not support his rebellion and so were not considered part of "all the people who belonged" to him, because they lived to write some of the Psalms. Just as Abraham IS the father of those who keep his faith, Korah is NOT the father of those who reject his faithlessness.