Seems to me that there are a lot more female riders in London these days, and also on the designated cycleways springing up around the countryside. London is quite bike-friendly compared to many UK cities but riding there is still hazardous and there's plenty of abuse from other cyclists, let alone motorists. (See below)
I'm female, none of my female friends still cycle, though we have an excellent 10 mile off-road old railway-line nearby which is deserted for most of the week. Yet they'll happily pay for gym membership.
They don't really give reasons, but clearly there's 'something' about cycling in the UK which is hostile or unpleasant for women, and the many reasons are already posted in this thread.
I take my bike over to the Nederlands and France, and it's like a breath of fresh air compared to cycling in the UK. Motorists are polite and give you plenty of room; acceptance of bikes seems culturally normal, and I've never been bullied off the road which has happened twice in the last year in the UK, including being knocked off my bike in London by another cyclist. (No, he didn't stop.) That ended up with hospitalisation for a dislocated elbow and concussion.
There's the maintenance aspect. I learned bike mechanic-ing just to get away from my LBS, the only one in ten mile radius - who overcharged to the point of extortion: (£60 to fit a V-Brake cable) and laughed at my ancient French supermarket bike: 'It's a bicycle-shaped object.' The LBS probably isn't typical but it's definitely female-hostile.
I don't think there's a solution, but also, there are plenty of other sports for women to enjoy without the perils, inbred hostility and abuse, of urban cycling in the UK.