I'll throw in another speculation, what the hey! I recall that back in the bike boom of the '70s, there were a lot of European offerings that cropped up in US bike shops that we didn't understand...like the club special and the mixte. It's clear now that the mixte frame dates back to much earlier than 1972, but I had never seen one before then. The first ones to make an appearance in Cali back then were economy models and they came primarily from France with a few Dutch and Belgian models, if your LBS sold that sort. I recall going with my sister to help her find a "10 speed" that she could use as a grocery-getter and attach a child's seat for my nephew-to-be. The Dutch bike shop owner sold her a Gitane mixte (cause it fit her and was the right price) and I remember I looked askance at both the weird frame and some of the components (I was being a hard-ass for the benefit of my sis) and said I didn't like those "cheap hubs with the big wing-nuts on them". He gave me a quick lesson concerning how many TdF winners (legendary champions like Coppi) had ridden hubs just like them...I shut my mouth...Now I just guess that a lot of European makers had a bin full of low-cost hubs that came with wingnuts and these were spec'd on the lower-cost bikes for which a quick release would have been "too dear". When the Japanese bikes came along (and there were mixtes offered by many of them) the cost of some of these luxury details was low enough that the Nishikis and Univegas all had QRs and nobody thought twice about it.