Is this really an "issue"? I don't really see a problem with millennials or any generation inquiring about bettering their situation and rejecting it if it doesn't suit their lifestyle choice. If employers really were so frustrated with dealing with rejected offers, they'd start making their descriptions more detailed with their nonnegotiable terms.I have worked in the private power sector for many years. It has been common lately to get people fishing to see if they can get a little more, but they aren't interested in actually relocating for similar or slightly better compensation.
Millennials in particular have been an issue. After going through the entire process applicant's turn down offers because they think they're magically better than their experience and training reflect.
Don't get me wrong, there are plenty of entitled people around, but I think people should determine what their worth is and go find an employer that feels the same. I've turned down offers after going through the process. If the door of opportunity opens you should at least take a peek at what's on the other side and if grass isn't greener I don't feel a bit obligated to walk through said door.