Don't underestimate the power of costume. I once arrived at a conference that told the speakers "wear your shorts, wear running shoes, untuck your shirt, keep it casual." I did that for my first talk and it wasn't as good as it could have been. For the other two talks I went back to my "uniform" of dress shoes, dress pants, and a tucked in speaker shirt, and I gave better talks. I think it gave me a very tangible reminder that I was not rehearsing, I was not running the talk for time, I was really delivering it, let's go! And sure, logic would say that the hundreds of people sitting looking at me should have taken care of that, but being in "speaker costume" really made a difference.
While it may seem outrageous to suggest a software developer wear a uniform, I have many clients where everyone wears a logoed shirt, every day. It would be weird if the developers didn't. And once you start to do that, it gains power - when you put it on, you gain context for the day. It reminds you that you are at work now.
The purpose is presumably to remind everyone that you are all part of the same team. That even though you don't meet customers, you are still working to meet their needs. That even though you are not at a front desk or in a store, you are a colleague and team-mate of those who are. That you are not different and not special (which is precisely why we resist it and say "not developers, surely?").
As a side effect it eliminates issues of dress code (is this outfit too sexy for work?) and might save time and effort for staff. Plenty of developers would be happy to wear the identical outfit every day and never again decide what to wear.
On balance I would prefer not to have someone else choose my clothes. But I understand the reasoning behind it.