Why are there so few mixtes with drop bars? The vast majority of mixtes around me have northroad bars. I can also find some nice old step-throughs with drop bars, but only mixte frames have that mixte look.

Normally I would assume this means that noone built that frame/bar combination, but I found a Motobecane catalogue from around 1979 that shows a mixte version for most of the dropbar models (I would link it, but I can't yet).
So where did those bikes go? I can find a lot of Motobecane mixtes for sale, but they are 95% northroad bars.

The reason I am asking is because I got my SO into vintage bicycles by showing her mixte frames ... now she likes them, but does not like northroad bars.
I did not expect this to be this much of an issue.
If I can only find mixtes with northroads, would there be any issue in converting to drop bars? I know that flat to drop bars requires a different stem, levers, etc. and still leaves you with a weird geometry, which I would rather avoid.

Additional information:

• I am looking for something suitable for Eroica, so 70s-80s
• I am located in Germany (maybe not many people in the 70s/80s here afforded high-end bicycles?)
• so far I have searched on the local Craigslist-equivalents, namely 'Ebay-Kleinanzeigen.de' and 'Marktplaats.nl'
• I was not alive back then to know wether people just disliked mixtes