It seems only logical that if an employer wants to hire someone for a job that they would naturally advertise or at least post the position on their company website. Why not cast as broad a net as possible to get the pick of the best?
After all, advertising a job on a number of job boards is pretty cheap as a percentage of your typical professional wage. Plus, the investment in every employee after hiring someone costs even more.
If an employer adds up the hours of training, company resources and the time it takes to ramp up a new employee to be a consistent productive performer you would think a little up-front investment to get the right person would pay off. It would make sense then, to choose from a large pool of candidates to have a better chance of getting it right. Right?