Not all browsers make it easy to turn DNT on (Safari has apparently removed it), so it's not an ideal opt-out mechanism.
DNT is basically a failed technology; if you really care about not being tracked you would just block the trackers rather than asking them to pretty please not track you.
(Edited to add: as others have said, this should not be opt-out anyway. Opt-in is much less user hostile, and as far as I know is legally mandated in the EU anyway.)
DNT is basically a failed technology; if you really care about not being tracked you would just block the trackers rather than asking them to pretty please not track you.
(Edited to add: as others have said, this should not be opt-out anyway. Opt-in is much less user hostile, and as far as I know is legally mandated in the EU anyway.)