The long fight over Do-Not-Track followed a predictable trajectory: a detailed, meaningful pro-privacy system was subverted by big business, and then published as a "standard" that offered virtually no privacy protections.
Today, turning on the Do-Not-Track setting in your browser does virtually nothing (Medium and Pintrest offer some support, everyone else not so much).
EFF's Privacy Badger blocks ads from companies that don't comply with Do-Not-Track, so running Privacy Badger is a way to give your browser settings some teeth.
The biggest obstacle was advertisers who didn't want to give up delicious data and revenue streams; they insisted that DNT would "kill online growth" and stymied the process. (You can chart the death of Do Not Track by the declining number of emails sent around on the W3C list-serv.) By the time the debate was winding down at the end of 2013, it wasn't even about not tracking people, just not targeting them, meaning trackers could still collect the data but couldn't use it to show people intrusive ads based on what they'd collected. The inability to reach a compromise on what DNT should be led sites like Reddit to declare "there is no accepted standard for how a website should respond to [the Do Not Track] signal, [so] we do not take any action in response to this signal."
To demonstrate their theoretical support for DNT—or from a more skeptical perspective, to garner some positive press—Google, Microsoft, Apple, Mozilla, and others started offering the "Do Not Track" option in their respective browsers, but absent a consensus around the actions required in response to the DNT:1 signal, these browsers are just screaming for privacy into a void.
"It's really sad that companies are not listening to their users and put weak and misleading pretexts to not respect their choice of privacy," said Andrés Arrieta, tech projects manager at the Electronic Frontier Foundation, who attempted in 2017 to breathe life back into Do Not Track by establishing a new standard for what websites should do when they see someone send the DNT:1 signal. (Everyone ignored it.)
'Do Not Track,' the Privacy Tool Used by Millions of People, Doesn't Do Anything [Kashmir Hill/Gizmodo]