I'm sure they have all kinds of athletic trainers, nutritionists, and exercise scientists doing all sorts of things.
The problem is there's a difference in results vs. how you train. How you train has a very real physiological response in your body that may not match up with what's best for you physically in the long run.
Baseball is maybe the best example of this, or at least the baseball pitcher. The pitching motion is an unnatural one, with some pitches being even worse than others E.G. the splitter. The training is functional to performance, and that comes at the cost of increased risk of injury
You can teach all the proper strength training, nutrition, and stretching in the world and guys are still going to blow their elbows out. In todays game, they're getting to kids younger, they're getting them into pitch labs, and they're getting more velocity and more spin from today's pitchers than every before. The downside of this has been the uptick in injury.
Proper stretching and strength training to reduce the likelihood of injury isn't moving in lockstep with the increased pressure that throwing a splitter faster does to the human elbow.
I think it's very easy for someone, who doesn't feel like jumping in to take a look at everything under the hood to just say something along the lines of "players just aren't built like they used to be"
I don't believe that. The average athlete today is much stronger, bigger, and faster than they were just a few decades ago. To reiterate my earlier point - Sports specific training is functional to that sport, and at times that can be at the cost of increased risk of injury over the long term.