I actually don't believe it.
Most people work not only for the pay check but also for some concrete project they want to see completed (or a customer problem they want to see fixed, etc). Omo economicus is a very simplified theoretical model of only one aspect of work.
There are options other than "loyal to the company" or "always choose option which pays most"
For example someone might like their co-workers, enjoy the projects they work on, and want to see the current product (that they have invested so many time into) succeed. But at the same time, they might not care about company itself at all. If the project got closed and co-workers left, they will move to a new company with no hesitation.
