The dating market is the best example of Gresham's Law I've ever seen

In economics, Gresham's law is a monetary principle stating that "bad money drives out good". For example, if there are two forms of commodity money in circulation, which are accepted by law as having similar face value, the more valuable commodity will gradually disappear from circulation.
It's why you can never find someone decent to date. They are the "good money" and they all got locked down at age 19 by their high school sweetheart.