It is populism, nothing less. Listen to Classic Fm and you always get the same tunes coming up as people's favourites. The same composers go round and round. But this is because they are great and emotive and all the rest.
Only ad agencies these days seem to seek obscure music. When you are dealing with Gothic or large emotion, falling back on stuff that has consistently moved people is relatively wise. And of course it is less costly and far less time consuming that comissioning new works.
A fine case is the theme music from Gladiator by Hans Zimmer and Lisa Gerrard - it went straight into the classical music charts.