The reality is that pro ball is a grind and not every player is going to be able to handle the workload even though they've tried to build up the pitchers workloads up more gradually in recent years. Some certainly were damaged in HS and in college, but some just genetically are going to be injured when they take on a pro workload. Fortunately for some of them surgery will provide a long term solution. Others won't be as lucky. The other big factor is that the harder you throw the more likely you are to be injured and there's more hard throwers in pro ball so there are going to be injuries.