When a surgeon does an ACL injury repair, he has to take a lot of things into consideration. I mean, sometimes they add a prosthetic, sometimes they try to sew up what is there, and sometimes they simply remove the injured ligament.
If you were an Olympic-class athlete in your prime, then they would want to do some procedure to get you back on your feet in record time. You probably only have a few years of prime performance, anyway. So, they often pick a procedure that gets very good short-term results. However, maybe it also loosens up a lot after a few years and sometimes things have to be re-done.
In contrast, if you were a 70-year-old granny, then they would pick a different procedure to minimize initial discomfort, but it would not have to be tremendously strong in the long run.
Many of us fall into the category of "weekend athletes." So, they don't mind if they leave the patient incapacitated for a few months as long as it gets them back to their normal sports and lasts for a few decades. In my case, they removed what was left of the severed ligament, and then took a few "nips and tucks" in several different aspects of the joint, and this tightened up the whole thing to the point where flexibility was hard to regain for months and months. But, that got good long-term results. Now, 27 years after the fact, I have to stop and think about which knee got which procedure.