Fame
Clowns are one of the few groups of entertainers that don't have many roads to fame. After all, that twenty pounds of thick white makeup makes it pretty difficult for anyone to know who you are.
The few clowns who reach fame (for example, Bozo) do so via their persona, but even then it's an uphill battle. It's been awhile since a clown rose to real prominence, so unless a new fast food joint opens capable of rivaling those golden arches, you're probably stuck being known (but adored) for an hour at a time by roving groups of small children.