How much do you challenge your hip motion/mobility past sitting in a chair? Your body is indeed very "use it or lose it" and what happens over time is that our hip joint capsules 'tighten' and we begin to lose isolated hip motion. This may initially appear as "feeling stiff", chronic tight hamstrings, chronic tight pigeon pose, etc. This growing stiffness and loss of flexibility is not simply because our muscles are 'getting tight', it is a response to losing hip joint mobility.
Do you stretch endlessly, get regular massages, endure Rolfing/deep tissue because you have chronic tension in your hamstrings, piriformis, quads, etc.? The reason for temporary relief in the above issues is because your hip joint needs mobilization and your joint capsule needs some stretching to allow those motions to actually occur within the joint first to prevent it stressing peripheral structures!
Best physical therapy practice involves treating the core of your issue, but also incorporating lifestyle changes to prevent need for future surgery as well as prevent reliance upon your practitioner for relief.