They've been around well over a hundred years, have been cultivated and adjusted with time by people considered etiquette/manners/social experts.
If one is hosting an event they have full authority who they want to invite, full authority as to what dress code they want at their event and decide what rules of etiquette they wish to breach.
I think when hosts determine their event they take everything in consideration including that some who don't appreciate the parameters of the event may not come. It is okay if you don't go, I've skipped more weddings than I have attended for various reasons. In my own and DD weddings we decided who to invite (yup some were mad), we set the dress codes and we breached some rules.
Host can set their own "rules" for their event
and
Guests can determine if they will attend or not.
All is good.
If someone/business is setting a standard for their own event, and a guest/attendee decides to do something opposite or unwanted, then it would be tacky (not in good taste). Tacky isn't just a "style" like gaudy but it's a behavior. It doesn't matter to who, it only matters to host.
Yes, hosts determine the dress code but it would be helpful if hosts study up and understand what they are saying. In OP situation they are technically hosting two events: a daytime wedding and a nighttime reception, with substantial gap in between. It would have been more helpful to acknowledge there are two dress codes or at least make sure the formal is attached to reception only. If there were no hours long gap of time, or change of venue then I could see a one dress code situation, but not here.
Yes, black tie is black tie and there is no real variation in what it requires. A gown is a gown, it is not a maxi dress or sundress neither of which would be okay in the evening event ... so again, too bad hosts don't understand.
SO INTERESTING how hard this seems to be for hosts and guests when a simple google makes it quite clear what the differences are and how one should dress. My DD had a vision for her wedding, it was a night wedding, very formal decor yet in an old factory building, served appetizers cocktail hour, full meal, full bar .... and she would have loved all the ladies in long dresses or fancy. She def wanted men in suits, not casual. But she put herself in shoes of guests and went with Semi-Formal and hoped men would at least be dressed up, preferably a suit. Most did. A plus one showed in cowboy boots, jeans and cowboy hat .... yup he was stared at by many. Once he was dancing he fell into the entertainment category. She didn't let it upset her but yes, it was tacky. [Note: He was a rodeo rider so maybe his date didn't explain to him the dress code or that we wouldn't have horses.

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Hopefully not a last minute emergency where you are on a YES list and they can't adjust their numbers. Just RSVP no right away, no reason is ever needed.
DD had about 15 people RSVP yes then not show up. Food costs alone were around $900 and that doesn't include the bar.

I've ALWAYS said no one is owed an invitation to a wedding and shouldn't expect one. I do not expect one from anyone except my own children. As a host no one should expect someone they invite to attend their wedding as there are many reasons they can't/won't attend. There are no obligations either way.
I have other personal wedding thoughts but that's a whole other ball of wax.