But why would one skip over brilliant engineers who are not so desperate? What the desperation brings to the table for the employer and why is that so important?
You need a certain fraction of people willing to just do the required work without complaining -- there is only so much schlep a person can tolerate; certain factors like marriage, children, a mortgage, sick parents, and sense of duty can raise the amount someone can handle. There probably aren't enough slots internally to accommodate the others. Compliance is a very useful trait for employees to have, obviously it falls on a spectrum.