Why doesn't God heal?

If I believe Romans 8:28, that God sovereignly orchestrates all events in my life for my ultimate spiritual good (and preeminently for his ultimate glory), I can only conclude that, all things being equal, if I'm not healed it is because God values something in me greater than my physical comfort and health that he, in his infinite wisdom and kindness, knows can only be attained by means of my physical affliction and the lessons of submission, dependency, and trust in God that I learn from it. (Storms, C. Samuel. A Sincere and Pure Devotion to Christ: 100 Daily Meditations on 2 Corinthians. Vol. 2. Wheaton, IL: Crossway, 2010. Print. 236)