Look at it from their perspective, let's say they're 5'4 135lbs and a 5'10 185lbs guy asks them to roll, they're giving up 50 pounds to him, and additionally giving up muscle density and size. That'd be like the 5'10 guy going to a gym full of 6'4 235lbs guys that have more muscle density and mass.
I'm the big guy at my gym now (as previous bigger guys have left) and I know to roll with certain people certain ways, it's what I do in almost every roll in the gym, but I still have guys that don't roll with me because they see someone that has 50+lbs on them. It's cool, I still get 7+ rolls a night, it doesn't affect me, but I have a feeling those same guys are on places like here, reddit, facebook, etc. saying things like this that females need to drop their ego and roll and be willing to get smashed.
TLDR: If you've ever ducked the "big guy" at an open mat or during drilling, you have no room to talk about females needing to roll with guys.