I know how eligible is always used in the context with these royal celebrities, but I never understand exactly what it means, if that makes sense.

The "eligible bachelors" always seem to be the popular young rich males, but I have continually failed to grasp a clear formula for what it means, and who precisely the media decides is "eligible". It all seems to be very random and based on the "it" people of any given moment, as decided by the commercially-driven media industry. Who sells? I guess that's how they decide who is eligible..... but I don't know.... I don't have a clue!!