Because they lack sophistication?

>The current market share of jazz in America is mere 3 percent. That includes all the great ones like John Coltrane and the terrible ones like Kenny G (OK, this is just my own opinion).

Well, in a populist culture without an aesthetic hierarchy, where you can't rank Kenny G as terrible and Coltrane as great without having to explain yourself, what place there is for jazz or anything more demanding than triteness for that matter...