We read old physicists if we want to do original research on the history of physics. Or maybe if we are studying an aspect of physics so obscure that nobody has covered it in hundreds of years. If we want to learn physics we read a physics textbook. As far as I know, the story is similar in math, chemistry, engineering, economics, and business (though maybe some other subjects that I know less about are more like philosophy).
Yet go to philosophy grad school, and you will read original papers and books by historical philosophers. Research projects explore in great detail what it is that Aristotle actually said, thought, and meant.
After some exploration, she proposes this:
Reading Aristotle describe his thoughts about the world is like watching Aristotle ride a skateboard if Aristotle were a pro skater. You are not getting value from learning about the streets he is gliding over (or the natural world that he is describing) and you should not be memorizing the set of jumps he chooses (or his particular conceptualizations of the world). You are meant to be learning about how to carry out the activity that he is carrying out: how to be Aristotle. How to do what Aristotle would do, even in a new environment.
An old work of philosophy does not describe the thing you are meant to be learning about. It was created by the thing you are meant to be learning about, much like watching a video from skater-Aristotle’s GoPro. And the value proposition is that with this high resolution Aristotle’s-eye-view, you can infer the motions.