If you care about how someone dresses when you hire them, odds are you're using bad criteria for your decisions. That's not to say that you can't get great people, but you're probably paying over the odds for them, if "dresses nicely" is one of your factors for selection.
I think I will hire better if I dont care about dress code - I think odds are better that I will find a good hire if one of my criteria is not "do they own a suit or a dress".
Funnily enough, all the programmers I know who "don't care about dress" also will say that they have negative perceptions of people turning up in a suit for a programming job.
They care about dress, they just want people to conform to a very casual dress code. Which would be fine, if they admitted to it. Instead, they say they "don't care about dress".
That said, it's a very reliable indicator on almost all situations, the most important exception being during an employment interview; it's extremely noisy then.
or that they expect to be around people who (act as if they) care about dress.
I disagree with this.
Showing up in "a suit", in most cases, isn't caring about dress, it's thinking that a required formality of dress is necessary. People that care about clothes, and are fashion enthusiasts, will show up in Thom Browne, CdG, Engineered Garments, etc. - or even just basic Club Monaco-type stuff if they're don't have a giant amount of disposable income.
While adherence to arbitrary fashion formality levels may be an indicator of unawareness, an interest in fashion seems incredibly unrelated to programming skill, unless the programmer is expected to be solely interested in programming - in which case, they should also rule out runners, rock climbers, guitarists, etc.
It's people that care about how others are dressed that are the problem. What you call "thinking that a formality of dress is necessary". We disagree on terminology.
"Looking the part" can be a lot worse than just clothes, though. Because most programmers are young white men, HR people, even women, even when they care about hiring more women and minorities, still tend to hire people who look the part, meaning more young white men.
Maybe getting rid of all pressure and expectations to "look the part" would be necessary to finally get rid of these subtler, subconscious forms of sexism and discrimination.
Also, we demand hipster beer to be delivered to our desks on Friday afternoon.
In my experience, that's not true. Many do care, but a significant part of it is caring about giving the impression that they don't care, coupled with the need to not stray outside the uniform. many places say they don't have a dress code, but that's usually short-hand for "you need to look like us to work here".
I really don't care.
Edit: I'm sitting in a very nice office!
All of which you need as a software developer.
I've never seen any correlation.