I think it's easy to figure out - and understand - the roots of the difference: black tie events, via the enforced dress code, socially permit the eccentricity of wearing of anachronistic items like Black Tie. However, the context of wearing Black Tie these days is socially completely different to the role in had before. It's no longer night-time formalwear; it's a party costume. Another example is wearing morning dress to a wedding: common enough, so the costume retains a certain modern social acceptability. But only within that context. You wouldn't wear it to work instead of a suit. These formal dress codes have become costume dress instead, and they're only acceptable when worn to an appropriate costume event. Sad maybe, but true.
Wearing anachronistic clothes items in normal daily life also has a costume effect; many dislike being thought of as wearing a costume. Myself, I don't mind that tag (in moderation anyway; or rather, I want people to think it's an stylish costume), so I do occasionally wear anachronistic items. But not everyone has a lifestyle that permits that flexibility, and more would probably not want to project that image in the first place. How can it be judged what is anachronistic and what is not? No hard & fast rule; it's based simply on what the average person in your intended circle of contacts thinks.
You wrote your post at the same time I was writing mine, and there's a lot I agree with in it and tangentially echoed (from a different angle, admittedly) in my preceding post.
However, I do think you're heavily romanticising the role & meaning of historical Black Tie in this quoted excerpt from that longer post of yours. Black Tie was simply a semi-formal dress code used for dinners between people from a certain class. Uniformity was not desired in order to create equality, but rather to define the boundaries of the event (i.e. "it's dinnertime, and this is what we do at dinnertime"). Remember, this was a dress code that at one point was adhered to even within the privacy of one's own home in certain circles, more worn out of a sense of obligation, duty and routine rather than with the aim of fun or inclusiveness. Now, it DID become what you're talking about, but only, I'd suggest from (roughly) the '60s onwards as people latched on to the idea of (to use your phrase) a festive elegant dress code to distinguish the gradually increasing informality and variation in the rest of their dress.
Nowadays, it is largely an instruction to follow a specific costume party theme (which, incidentally is what positively encourages greater deviation from the standard, and gives room for personal expression. After all, if it's just a costume, you can riff on it how you like and it means nothing). I will leave it to others to debate whether this is a good or bad change (actually, I'm pretty agnostic on that issue. I'm not sure whether having worn black tie fairly frequently makes me more or less likely to side for or against, actually).
