As someone who spent years in feminist activism and has now left that movement (although I still support their goals, I just have decided to spend my energy in a different way) - I think one of the reasons for dissociative feminism is compassion fatigue, caused by a hyper-outraged response to a constant barrage of news articles and clickbait headlines, tweets etc that all need a furious response. If everything is outrageous, one's emotional response to truly horrific things becomes dulled.
There was a time where my Facebook feed had become nothing but outrageous headlines, anger and rage inducing. I would spend hours and hours on angry online debates, everything needed a response, and I needed to be right every time. Silence is violence!!!
But after all, not everything can be responded to. And online response is inherently dissociated from the real world.
Eventually I found myself becoming so numb I was unable to find myself emotionally reacting to stories of rape and torture and murder of women, stories that would in the past have made me genuinely sad. I looked at the headlines with dulled eyes and no feeling whatsoever. And yet I still posted an all caps "THIS IS SO EVIL" kind of response with lots of exclamation marks, performing an emotional response I was no longer capable of feeling.
That was compassion fatigue. It was so damaging to me I had to take six months off social media entirely, and I've never really returned to online activism. I now try to focus on helping people I can interact with physically, and I've become less dissociated, but I can absolutely see why dissociative feminism has developed. It's a symptom of compassion fatigue, a defense mechanism of a mind overwhelmed by a constant barrage of stories designed to trigger peak emotional responses.