Having have a couple of medicals now, I am realising that the AMEs actually know quite a bit about the medical aspect of flying!!! This knowledge when combined with the answers to these apparently nosey questions allow the AME to offer specific advice, as well as assess your fitness to fly.
You can surely appreciate that someone flying a high-performance complex aircraft with an oxygen system, and who also smokes has a higher risk of a hypoxic incident than a smoker flying a microlight. The AME may suggest giving up smoking to one pilot, and not to the other.
These questions give the AME the background information they need to provide a full service to both yourself and the CAA.