If it was not medically necessary, I imagine there would be no insurance coverage
Medically necessary is subjective. Most of the people who get surgery aren't in mortal danger from not having the surgery -- it's all shades of grey. You'd merely need to have a surgeon who agreed that surgery would significantly improve your quality of life.
That said, I see the reasons as two-fold:
1) Some people go into complete symptomatic remission on relatively benign medication. I'm talking about
a REAL, durable remission, where you poop about
once a day and eat what you please and don't have urgency or pain. We don't seem to see a lot of these cases on the boards, but that's because those people don't waste their time on UC message boards. As noted upthread, a colon that works 100% perfectly, which IS achievable through medication for some patients, is always going to be better than a well functioning j-pouch or ileostomy. I love my j-pouch and I have no regrets, but if I could magically have a perfectly functioning colon instead, I would prefer that.
2) Every surgical procedure has associated risks. The risks vary depending on who you are, where you are in life, your comorbidities, etc. For example, an obese smoker has "more to lose" by going straight to surgery because any surgery is going to be more dangerous for them than a non-smoker with a normal weight. Another example is women of childbearing age. Even if I knew in advance that my j-pouch was going to function great and I wouldn't have complications from surgery and it would put an end to my UC problems forever, I would be hesitant to go straight to surgery because any abdominal/pelvic surgery increases the risk of infertility.
dx'ed UC pancolitis 5/12
past meds: asacol hd, VSL#3, apriso, rowasa, xifaxan, 6mp, cortifoam, pentasa, cimzia, canasa, butyrate, flagyl, cipro, prednisone, remicade, methotrexate, cholestyramine, cortenema
current meds: none!
step one: colectomy, end ileo 1/16/13
step two: j-pouch construction, loop ileo 5/1/13
step three: takedown 7/31/13