I’ve never been big on dress codes, as I pointed out a few days ago. But they do have a place, and in congress, part of that place is to try to preserve some small sense of decorum in what are supposed to be serious legislative bodies.
The problem with relaxing longstanding dress codes inevitably becomes that there is a subset of the culture at a company or other entity that has no sense of decorum, which is why the dress codes had been implemented in the first place. I was working at a company in Austin in the mid-80s when casual Fridays started becoming a popular thing in corporate America. The company management decided to adopt the practice, and within a month, we had certain people showing up to work in cutoffs and flip-flops showing off their mangled toes and hairy feet.
Within another month, the company had issued a new dress code for casual Fridays that specified no cutoffs or flip-flops were allowed. The sad part was that they had to actually say it out loud because they had hired people who were too clueless to figure it out for themselves.