Maybe not a single browser toggle, but it really should be handled at the browser level. There are browser APIs for opt-ins like your current location, using the camera and microphone - why not one for tracking consent?
The problem isn't technical - the problem is that ultimately spyware operators want to track people so it isn't in their interest to support these solutions and won't do so unless they are forced to. Since enforcement is significantly lacking, operators adopt the pragmatic strategy of non-compliance or pseudo-compliance with the current banners.
