Huh! That is really surprising to me, not least because, as you say, our tastes overlap reasonably well, and I'd expected this would be one of the places... It occurs to me, though, that what I really liked about Cotillion was that it upended tropes I didn't like (in particular, the Reformed Rake) while using tropes I did (Fake Engagement). Also, I really liked Freddie. And I can see that those might be somewhat personal idiosyncrasies.