NY-LA, why is flying cheaper than Greyhound?

I happened to see one of those spanking-new modern Greyhound buses
this morning. It even had Wifi onboard(!).... (at least the sign on the widnws
claimed so) Add to that the Sopranos re-run I saw today....

Could get it out of my mind.... so I just looked up Greyhound for travel from
NY to LA.... I was amused to find the roundtrip fare is more expensive than
flying.(assuming advance purchase)

Other than Janice Sopranos(who rode from Newark to Seattle after killing her
fiancee), who else rides Greyhound on trans-con routes?