I used to wear them all the time in Denver. But it's usually at least 5 degrees Celsius cooler here than London, rains more, is more often windy.
I think I wore them once this year. Ditto open toed sandals.
When I came here I had loads of flip flops, Tevas, Birks, Choco sandals. I got rid of them all when my feet went up a half size after having a baby. Just not a lot of use for them here . . .