It's the complete opposite. What killed DNT is Microsoft adding it to their browser and set it to true by default, pretending they cared about their users. Doing so, it was not the expression of the users anymore and so web developers ignored it, and so it died.

It died because companies had no incentive to respect it. The writers of the GDPR could have easily added a single line saying you had to respect the DNT header, but they chose not to.