I agree with this.
Every place I’ve worked we had a dress code that we were expected to stick to which was pretty much along the lines posted by OP.
And that’s for the reasons that PP have said - once one person wears a vest, then you get another person wearing a skimpier vest and then you get into stupid arguments about what level of vest is ok. It’s clearer to have a blanket ban so there’s no ambiguity.
OP, you already asked what’s wrong with showing your thighs at work or your armpit hair. You’ve taken it really personally as if it’s your body that’s somehow the issue. It’s everyone’s body - lots of places have a dress code for a variety of reasons. Clothes that flash thighs or armpit hair - on men or women - has never been viewed as suitable attire for a professional workplace.
It just reminds me of the “bring your whole self to work” mantra that’s become so popular. I don’t need or want to know everyone’s whole self, just their professional self. And along those lines, you can’t just wear what you want because you like it. Working clothes should be reasonably professional even if you’re not customer-facing, unless your dress code explicitly permits its casual attire.
If your workplace is hot then lobby for more fans, shades, or other things that will make a tangible difference to your comfort. As PP have pointed out, in hot countries people don’t wear less to stay cool, they wear loose, flowing clothes. Win win for both employer and employees, surely?!