I think it's probably just "people younger than us" who want unisex loos. Not all of them of course, but enough to notice.
Serendipitously Greg James and Mollie King mentioned it in passing on Radio 1 yesterday; both saying they think it's time we all just had gender-neutral.
I can't find any age-related stats, but it was a find of the youth consultation report in Ireland, December 2017:
"A strong message from both the survey and the consultation events was the need for gender-neutral bathrooms and changing rooms."
Here's an article about that titled "Young people want better sex education, gender-neutral toilets and LGBTI history taught in schools".
Oh, and parents with children; apparently they're quite keen on unisex loos. I was trying to work out who wanted unisex loos the other day and read the following:
"Another benefit of unisex bathrooms is that they make it far easier for parents to accompany children of the opposite sex to the bathroom. Most men would feel uncomfortable entering a women’s bathroom, and vice-versa; the only alternative is to let children use the facilities unattended. Although it’s rare, leaving children unattended in public bathrooms can have tragic consequences: in 1998, a nine-year-old boy was murdered in a public restroom when his aunt decided to let him use the men’s bathroom alone."
So I guess the architects/developers etc. have good a few different perspectives to consider.