Same question - why can men not understand feminism? If you’re not experiencing a specific oppression it can clearly be more difficult to see that oppression, and therefore the need for a movement to counter it, but it doesn’t follow that you’re therefore incapable of understanding the issues once you do see the oppression and learn about the movement.
I think that I have a good imagination, I've been an older sister, older cousin, I've baby sat, I read all around the subject. YET, having my own baby was a whole different ballgame, it gave me an understanding that I could only gain through having that experience.
Just like I could live in Spain for 30 years, speak fluent spanish, marry a spaniard, but still, not have a depth of culture that would have me unquestioningly mop the street outside my house, like so many did when I lived there - I could know why they did it (Franco), but I didn't have it etched on my soul.
Men can have a superficial understanding, they can read all the theory, and speak it fluently, but they haven't lived it. They haven't, from birth, been given dolls, been expected to be the peacemaker, or to help with the housework, been ignored in B&Q, or become the default contact for a MIL. They've not had expectations around childbirth and child-rearing, been ignored at the doctors, when complaining, been grunted at for taking up space.
There are some things that you have to live to truly understand.