Driven by irrational exuberance.
When I was growing up reading Outside Life and Field and Stream in the 60's and 70s, there were always articles on the advantages of fishing wet flies for trout. They explained that trout feed 80% of the time subsurface so you were better off fishing wet most of the time. And they weren't talking about indicator nymphing either. They were talking about swinging the classic patterns with a paired duck wing section tied swept back and a soft hackle collar or throat, e.g. the lead wing coachman. It seems like the only wets that have survived from that era are the soft hackles. It seems like diving caddis patterns are a newer idea that resemble the classic wets. Perhaps the classic wets were imitating the diving caddis life stage.