This is something people make a far bigger deal about than it is. It's actually not illegal in most places in the US for women to be topless in public.
(Also Minnesota should be light blue as well.)
It's actually been legal in all of Canada for almost 30 years because of a Canadian Supreme Court decision...and guess how often women are seen topless in public in Canada. It also seems the majority of Canadians aren't even aware of this.
So it's almost entirely a social expectations thing than a legal thing.
I find it interesting how little correlation this map has with evangelical populations or whether a state is red or blue.
Probably because in mainstream politics it’s a non-issue; many of these laws were likely enacted 50 or 100+ years ago and no one has bothered to change them.
Some of it also probably has to do with court decisions that nobody bothered to punt up to SCOTUS, since women do sue about this occasionally even though it's not a high-salience issue. I think Utah is in yellow rather than dark red because of a Tenth Circuit decision, for instance.
On that note I was slightly incorrect about Canada, the 1991 decision came from the Canadian Court of Appeal (they apparently only have one), and never reached the Supreme Court of Canada. So if any province or municipality wanted to challenge this to the Supreme Court of Canada, they could in theory, but it's such a minor low-salience issue this has not occurred in the 30+ years.