The way I read it was that granny squares saw a cycle of popularity, rather than crochet in general. 40 years would be a pretty normal length of time for something to be cool, then dated, then cool again.

Personally, I learned granny squares and mile a minute afghans from my mother. Until the last 5 years or so though, I definitely saw them as old-fashioned and out of date. Now they're coming popular again with different color combos and I'm coming back around.