It's the expectation. Somebody has mentioned birthday cards. Yes, it takes two minutes to write them. It's not the doing, it's having to be the one who does the remembering.
I haven't really got a big mental load as I don't have children and I am not married to the sort of man who thinks it's my responsibility to book him in at the dentists, or send his family cards.
It's a bloody good job because I'm not great at remembering birthdays, or remembering to look at the book I wrote them down in.
I used to get a lot of grief from my father when I forgot a family member's birthday. How awfully selfish I was, etc.
He shut up about it when I pointed out that I had NEVER received a birthday card in his handwriting. He was there when I was born, yet he delegates the task of sending a card to his wife, who is not my mother. So I am selfish and indolent for not sending cards, but he's never done it. Because he has a wife.
And that, to me, is the problem in a nutshell. It's not the tasks, it's the expectation, and where the blame falls when it isn't done.
If you have kids, if they don't get to appointments, if they don't have clean PE kits, etc, who is still seen as responsible?