I actually have to say I see it from the doctor's perspective a bit - I have two close friends who never wanted children including my best friend from the age of 11 who even then didn't want them.
People always used to say 'oh she'll change her mind' and it used to always really annoy me as she was always consistent and knew her own mind. I don't think she ever looked into sterilisation but she had long term contraception that worked well for her so it was never an issue. Except, in her mid-thirties, she did change her mind. As did the other friend, though she was a bit older.
My first friend's explanation was that after ten years marriage to her husband he started to think a child would be nice. She knew at that point he would step up, and do the majority of parenting, and that she had enough money and was advanced enough in her career to fund childcare, and one of the main reasons she didn't want children was because of her career focus so she went for it. So far is sticking to one child.
The other friend is a bit more bizarre: her and her partner were both adamant they didn't want children, then she was told at a hospital appointment out of the blue at 38 she was about to lose her fertility and if she wanted to have a child she'd need to do it in a six month window and somehow that made her decide to give it a go. They've also only had one child.
I knew both of these women for twenty years as they were sure they didn't want children, and would have supported them in choosing sterilisation if they wanted that. I've also spent some time on conception boards and been staggered by the number of people trying to conceive with men who have had vasectomy reversals. So I guess, a lot of people must change their minds. I'm not at all saying you're one of them, but I suppose from a GPs point of view they have no obvious way to tell who will change their mind and who won't.