Gosh, I'm not sure why they push PT... well... actually... it's because PT is a BIG money maker. I recall a dinner with the director of a regional hospital group who predicted, back in 1993, that PT would be a billion dollar industry in that region alone. He was right. At that time, PT was hospital and sports based. Since then, through outpatient PT facilities, it's exploded even more. It's a $30 billion industry in the US.
My OS wants all his patients to do initial PT because he wants to make sure they at least do some moving around right after surgery. If at six weeks he sees that the patient is doing well, he doesn't care about PT. My PT guy, though, wanted me to do another 20 weeks! Why? Because my insurance would pay for that much. Only reason. My OS was fine with me stopping it.
Don't get me wrong: PT can be quite useful. I'm glad I did it, because I think it did help me some. But the reason there is such a push to do more and more PT is more likely to be financial than because every patient needs that much.