Just about any site can use any data you provide them for anything regardless of what permission one gives. Asking them to do or not do something has the same effect as asking a mugger to not mug them. At best one would get a chuckle.

The partial exception would be if one has a mutually binding contract with said company and that company is made painfully aware that one has multiple law firms and infinite resources to go after them. They might adhere to the contract for a while until the company gets big and some new middle management want to take risks to look good for their management which means breaking ones contract behind their back.

There was such an standard, but it was ignored, because people don't want to be tracked, which is diametral to the targets of companies to get as much data as possible to sell you stuck you never need

This doesn't answer the question though. Like okay, everyone ignored "do not track". So the correct response is to make an even more annoying system that can also be ignored just as easily as "do not track"?

And before someone says the new system has a law behind it so it can't be ignored as easily as "do not track"... that is irrelevant to the discussion of "built into browser" vs "each website implements its own custom thing".

If we want to implement "do not track", all browsers need to prompt the user once (or once for every new incognito session) and save their settings. Instead, browsers turned it off by default and users don't know whether this exists in the browser.

Many browsers today are privacy first and by default will block trackers. Except that one browser by the company whose business model is reliant on ads.

The pop up seems to be some kind of UX decision to protest laws around this. These sites can function well enough without them and I doubt anyone ever clicks the button that says, "Yes, I would like to maximize the amount of tracking you use on me."

"do not track" is just that

But everyone ignored it and it just provided additional entropy for identifying you!