It's simple logic, people move because they can better deal somewhere else otherwise there would be no point. So if people move, the benefits aren't keeping up with other jobs they can get.

Most employees are not loyal, because they know companies are not. If they think companies are loyal, they are probably new to the job market. Once a project ends, and there's nothing else to work on they will get rid of you. There's no reason why employees should not think the same way.