That's the first and best question to ask when troubleshooting a system.
However, things get tricky when, as in the case of baseball and pitching/throwing mechanics and the epidemic of injuries, the change happened 10-15 years ago.
One common refrain you hear is that pitchers are getting hurt because they are being coddled; if the pitch and innings limits were removed and pitchers they were just pushed harder, their bodies would grow stronger.
The problem is that there are three problems with that argument.
First, back in the day, pitchers with good mechanics, like Sandy Koufax, still got hurt when they were pushed too hard. Second, the way ballplayers are being taught to throw has changed. Third, the way that pitching mechanics are being taught has also changed; the definition of Proper Pitching Mechanics is different. Pitchers are now being taught using a number of problematic pitching cues and drills. As a result, pitching velocities are up at all levels and pitching injuries are also up at all levels.
It's not a coincidence.
Up, Flat, Up, Flat, Up
You can see these differences if you compare the Timing of modern pitchers and pitchers who were both dominant and durable.
Matt Harvey, Tom Seaver, and Noah Syndergaard
Notice how the arms of older, great pitchers tend to be UP at foot plant and modern pitchers' pitching arms tend to be FLAT at foot plant? That's called Flat Arm Syndrome and it's a huge, and largely unrecognized, contributor to the pitcher injury and Tommy John Surgery epidemic.