Cultural innovation is a strange and wonderful thing.
Take one of the major cultural advances of the 1970s: the metal umlaut. It all began with Blue Öyster Cult, then came Motörhead and Mötley Crüe. But Spinal Tap went one better with an umlaut over the n. Brilliant! Take that you weedy vowel umlauters!
And then, cultural progress ceased. The design space of metal umlauting had been explored and exploited. Where could metallists go next? Umlauting every letter? So, progress petered out. The great umlaut stagnation set in.