.... your left ear doen't only get info from the left speaker, it does get info from the right speaker ....
But that is exactly what is NOT supposed to happed! That is why one easily get a more 'in 'situ' (ambience, whatever) awareness with headphones.
This bothered me from the first time that Harold Leak visited SA in the 50s to demonstrate stereo. In stereo photography you only get the real thing if the left image is viewed by the left eye ONLY, and vice cersa, since the camera lenses are situated where your eyes should have been - each lens represents an eye, and one only ...
Now we record sound with cartefully placed microphones where the ears should be ... and then we re-mix the lot by making both ears having to sort out left and right a second time. Thus it becomes mainly a phase thing instead of also being a loudness thing. As said before, using a table stereo loudspeaker setup, and then placing them so that one can go closer ending up with the head between the loudspeakers, the 'ambience sense' will suddenly open up as one's head moves toward a position where each ear mainly hears only the channel it is supposed to hear. (All this, provided the blinking recording is done right.)