@ampnaman From what I can tell, most of the medieval Europe-esque ones are apparently cribbing their settings from an otome game called Meine Liebe, in the same way that most videogame-esque isekai base themselves off of Dragon Quest and most RPG fantasy settings pull from Tolkien's stuff.
Oddly enough, many of the really famous games (like Angelique, Alice in the Country of Hearts, Haruka: Beyond the Stream of Time, and Meine Liebe) don't have English releases and info on them isn't easily accessible. It took a little digging to even be sure that Meine Liebe
was a dating sim—apparently it got an English anime release that cut out the heroine entirely and focused on the love interests, which the Wikipedia page reflects by not even having her listed as one of the series' main characters!