You gotta distinguish between “in an ideal world” vs. “in a world with horndogs and creeps.”
In an ideal world, plenty of women would absolutely go around topless in hot weather, and some would also do it as a form of fashion or standing out. And, indeed, lots of women go topless at home in those kinds of situations.
But in the real world, even if it were legal (which it usually isn’t), the patriarchy makes it impossible in this day and age. Until men who behave inappropriately are held to account for their crimes and bad behavior, the potential downsides of going topless are too high for the vast majority of women to be willing to accept.
However! There is safety in numbers. Things like nude races and parades attract many women; nudity is our natural state and there’s definitely no shortage of people who would enjoy having the option for it more often.