Not poor conditioning at the pro level, or perhaps college, but most likely the HS level when bodies are growing. Too many young pitchers lift more than they should, this eventually can cause too much stress to shoulders and elbows that already go through enough stress. it's accumulative.
I just read where a football player fell in spring practice and seperated his shoulder, now needs surgery to go in and clean out some tears. Injuries happen in every sport. Kids just play hard.