This is a fair point. However, keep in mind that loyalty to companies is generally one-sided: most firms will not hesitate to layoff staff if business goals/economics dictate.
Speaking for myself only, any loyalty I have is to people, not to companies. I'm loyal to my boss, my co-workers, etc. These are people I want to work with in the future, and it protects my reputation. Beyond that, I have no loyalty to a company for just the reasons you mentioned.
