It's not that they're "reviled", it's more like they don't really appease anyone. Clearly they're not aimed at men, so let's throw that off of the table immediately. Girls have so many other toy options than Minidolls. We have examples such as Shopkins, L.O.L. Surprise, Barbie, etc. LEGO just never really appealed to them despite the modern attempts to try to make the brand more neutral.
It also has some to do with playstyle. Girls don't want to build a dollhouse, they want to play with their dolls in it. They want to care for their dolls and roleplay with them.
Women toy collectors aren't as common as men toy collectors either, which puts Minidolls at an even worse disadvantage. Adults who like dolls can either collect regular dolls or make their own with all the custom BJD hobby shit out there.
Lego Friends also came out at an unfortunate time where most of the 90's Lego craze died out already and those that would've liked them were already too old to play with toys anymore.>Is it the fact their legs aren't separate pieces like regular minifigures
I don't agree because Polly Pockets were exactly like that and they were a hit among girls way back when. Then Polly Pocket got rebooted badly (twice), so now Shopkins has made their own version of the vintage Polly toys that are somewhat popular since Moose Toys has a lot of good thing going for it atm.