Morrigan was hot, that's why people loved her. We even see it in BG3, Shadowheart is as confrontational, especially towards Lae'zel but people are fawning over Shadowheart because she is hot.

But I think a lot of backlash towards Lae comes from people who don't know D&D. They aren't aware of how dangerous Mindflayers really are. And they also aren't aware of Githyanki and their relationship with Mindflayers. If you take these things into consideration the actions of Lae become much more reasonable.

Shadowheart's struggle are much easier to relate to. Which is part of the reason for people siding with her over Lae'zel.

With male characters people are more forgiving because they don't consider a romance option.