I almost never pitched, but I did throw batting practice once in a while and I got nailed in the shin by a line drive. Black and blue for weeks. I haven't played regularly in 15 years. Wife gave me a choice when kids came, and I picked soccer so I could stay in better shape. Also, my arm was shot. Now with kids' schedules I haven't played anything in over five years.
That is just a fancy way of saying, "the reason is money". There isn't a shortage of cows in this country.
If MLB wanted to open their own tannery or whatever, they certainly have the resources. Surely fans would pay more to purchase beef made with cows that provided their hides to MLB balls.
Passing on Rocker may have been a really good decision. Mets think something up with the elbow, deal in jeopardy: