The idea was that, given a significant enough amount of people turning it on, advertisers would take notice of it and react accordingly. If it's on by default it is meaningless.

It's a tool that enable users to send a message to advertisers that they are not okay with their practices. It was designed this way. It says you are okay with ads but not with the tracking.

> There are no incentives to do so, and no punishment or repercussions if they don't.

Except for adblock. If the only option to avoid tracking is to block ads, then that is what will be used.

Therefore, browsers should come, by default, with an adblock feature (or simply, just bundle the adblock plugin). This DNT business is purely just lip service.