When someone has a “mobility issue” it is often tied to other “issues.” For example, someone has an injury or experiences some pain in a position and the body compensates (consciously or subconsciously) to restrict movement around that position. There is a shoulder impingement that causes pain when the shoulder goes into flexion thus the body decides that movement is now off the table. Eventually these short term solutions to pain become long term restrictions.
Another side effect is that when a person decides that they need to use that range of motion for survival or sport, the body will find numerous ways to “work around” the issue. Instead of lifting the arm overhead into shoulder flexion the body will now compensate by bending backwards and creating undue hyperextension of the lumbar spine: a creative short term solution with bad long term repercussions.
This is all just to say that when dealing with “mobility issues” you have to address pain management issues as well as movement re-education issues. Unfortunately most people think like shoe salesmen, they see you run and then prescribe a shoe that will supposedly fix your feet. It doesn’t work that way.