I've just been diagnosed that I have a torn ACL and a torn meniscus. Could someone tell me WHY the orthopedic surgeon is recommending physical therapy before the surgery?

If you don't achieve full range of motion before your surgery, the rehab will be much harder post-surgery and it you might not regain full range of motion again.

I've torn my acl twice and my surgeon really stressed that I get the swelling down before the surgery. Both times I did that and I never had a problem getting my full range of motion back after the surgery.