I’m not a woman, but I would think flip flops would be very easy to put on (and take off if you’re in a culture where folks leave their shoes at the door) and they are also cheap.
And do these women have fancy manicured and polished toe nails? Unless they wear something like a flip flop, nobody’s going to see all the brightly colored nails. In that case, it’s the same reason a body builder wears a tank top—to show off all that hard work.
Like that picture above, those toes are fat as sausages, why would a woman want to let anyone see those?