Your concept of "holes" is just the state of the current job market for engineers. There are more open positions than engineers available. Hence, companies have

Your concept of "holes" is just the state of the current job market for engineers. There are more open positions than engineers available. Hence, companies have to compete more for the available engineers. Salary is not the only but certainly a major factor to make people switch jobs. At the same time the profession gets more attractive for "outsiders". We had this the other way around a couple of years ago in Germany: lots of electrical engineers and to few jobs.