Good posture is a rare and wonderful thing; your forward head posture is not. From my perspective everyone tucks their pelvis under which sends the thigh bones forward and the upper body backwards. While this isn’t good posture it tends to leave the head fairly well situated on top of it all (Left picture). Perception wise this seems important for the brain as I think most bad posture comes about to accommodate a head needing to feel “correctly aligned”.
When I put someone into the posture that I want them to work towards (getting the legs under the hips), the head is often thrust even more forward past the line of the shoulders and out into space. This doesn’t look any better than it feels. The forward head is situated so because of a lifetime of bad posture and imbalanced muscle tone left a skeleton that can’t support being put into the correct place. Getting the legs under the hips and untucking the pelvis often pulls tight lower back muscles into tight relief for which the upper back compensates backwards as the head moves forward. Over the long haul anyone can change this environment but it will take a good deal of time and conscious effort.
As a concept this might seem odd—good skeletal alignment messes up the head while bad posture allows the head to sit on straight—but the brain requires a certain feeling of normalcy. Keeping the head in a decent place at the expense of the rest of your posture serves the brain but nothing else as we make our way through life.
Take some time to assess your posture honestly and start working on the many little things you can do to change it.