When an employee makes a change in employer, for a better position, more money or benefits, they are often called ungrateful mercenaries. We see that publicly a lot in the sports world or on TV, when an athlete or actor holds out for a better deal or more cash. They see themselves as acting in their own best interests, but that doesn't matter as the team or production company resorts to smears and insults to sway public opinion.
There is even a notion of a "hometown discount", that a player should accept less from his current team when comparing multiple offers.
Why doesn't the reverse exist? Well, the answer is "it's just business". Those three words sum up the amorality of the business world. And those three words also cover up a lot of personal malfeasance.
The corporate culture is rife with paranoia. Executives holding on to their jobs depend on staying in the good graces of superiors, and fending off "challenges" from underlings, both real and perceived. The personal wreckage wrought from these activities is so very often obscured by those three breezy words, "it's just business".
With unions under attack as never before, there is even less hope for workers. The rarefied superstar athletes and entertainers can protect their self interests, but for the majority of regular folks, not a chance.