Why Misquotations Catch On

You've probably heard the phrase 'Beam me up, Scotty'. Or Humphrey Bogart's iconic 'Play it again, Sam'. They were never actually uttered. In the world of speeches and orations, especially historical ones, the persistent misquotation is understandable. If you're a journalist - especially in the pre-recording age, when all notes were taken by hand - you might then type that mis-remembrance into an article. Multiple versions circulate. And so on.
But in the modern age, where basically everything is track-downable, what's our excuse? Why do misquotes arise - and why are they so persistent and hard to eradicate?