Mobilizations for an immobile tissue will not last as long as mobilizations on healthy tissue because there is more going on.  The tendinitis is a symptom of something else that is going on. If you are not addressing the cause of the issue it will continue to occur.
You are unlearning one position/organization of an area and replacing it with a new position/organization.
It is the same as changing technique with a skill it can be tough to break a habit and create a new neuro pathway for changed technique or in this case position/organization.
If it is something that has been that way for some time it may take some time to get ahead of it.
Once you are ahead of it things move to a more maintenance based situation as the tissue is healthy again.