Mediocrity in and of itself is a contradiction. Why? Because most people and organizations who accept and endorse mediocrity get results that are actually below mediocre.
This is not surprising at all for me. When faced with the combination of low expectations and an actual desire to not achieve excellence, motivation goes out the window.
How did this happen? Growing up, did our parents, teachers, and coaches say "Good enough for government work"? Not mine. Mine, and the role models of many other people I know would say things like "If it's worth doing, it's worth doing well!" or "Effort beats talent when talent shows no effort." Many people still vociferously aspire to achieve greatness or to produce great results but their numbers across many disciplines appear to be in decline. Where did this desire to just get by come from?
Did it come from our cultures denigration of competition? Could be... We live in a society where "everyone's a winner", and "all children are special". This nonsensical crap gives people nothing to shoot for. Why try when all results are viewed as equal? Of course some self motivated souls still identify with the concept of doing anything less than your best is cheating yourself and that the reward is in the doing, but the implicit message of the role models of today must bear some responsibility.
Did it come from the disillusionment with the establishment? Could be... Our parents and our peers grew up where many people believed (erroneously) that their employers actually cared about them as people, that they were a part of some bigger vision and that a "job for life" was just that. When corporate corruption, treacherous leaders and over-eager downsizing became prevalent many from generation x and beyond have a different view of what the relationship between an employer and an employee should feel like.
Did it come from the complete destruction of accountability? Could be... My parents forced me to come clean no matter the implications. You were responsible for your actions and you accepted the consequences. How many role models in our society (all the way up to the president - and not just the last two administrations either) do their little verbal dances around any and all allegations no matter how trivial or how critical. Parents now actually lie and endorse lying to their children to avoid punishment or to gain reward that they are not entitled to.
In the end, I'm not sure where it comes from, but I can see where it leads to. The USA will more than likely continue its social, artistic and economic decline and as I said at the beginning, it won't stop at mediocre. Aiming for mediocre doesn't work. High expectations will more than likely get people's best effort out of them. Medium or low expectations often get the same thing - whatever they believe is the absolute minimum necessary.
Mediocrity = Crap.