See Prescribe regular walk for unfit patients, says GP - Telegraph
In the above report, a UK doctor who encouraged his patients to take up walking instead of taking prescription drugs for many ailments found that many experienced improved health eg reduced obesity and reduced dependance on antidepressants.
However, the medical profession is reluctant to follow this doctor's lead. That's because it is far easier to cater to patients' preferences for prescriptions instead of attempting to motivate them on the importance of regular walking.
Given the colossal costs of medical care, governments and medical insurers who fund most of the medical bills should pressure doctors to medicalise walking for ailments that could be cured or lessened by walking.