Baseball is not heart surgery, quantum physics, or any other field requiring deep thought.  Yet, what is painfully obvious to the casual observer appears lost on those managing.  You have some players who are kept around because of friendship and loyalty while others who have much higher production this year are held back. That's not a good business model in any endeavour. 
Not much different than car sales - you're only as good as this week or even today.  Doesn't matter what you did last year or last month those days are gone, repeat and strive tomorrow or hit the skids.