Well, if I were sick and needed treatments for a year, but the company hired me anyway, gave me the time off, and paid me full salary, I might feel a little loyalty.
But athletes are different. The feel entitled. In short, don't blame WM. The front office took a chance and signed him for x dollars over 4 years (or whatever), and had to understand that they were really signing him for x dollars for 3 years before free agency (and a year down the road to boot). Time will tell whether he was worth a #1, x/3 dollars a year, and only 3 years of service.