I'm far from a doctor so don't take my knowledge on the subject too serious, but my wife works as a nurse at a surgery center that does a lot of sports related procedures so these are they types of conversations I hear about from time to time. From my understanding (and its a very limited understanding) you're absolutely right in how strong these things are at least for the average human. The issue seems to be that they arent the most flexible and struggle with a lot of high impact twisting motions which is why they aren't more common for athletes. Couldn't tell you if thats a specific type of material that has those issues, all of them, or how many different artificial ligaments are on the market right now.