The rest of it is suggesting to the population at large there's such a high demand for these positions they should enter the market and pursue that career. The idea is to flood the market with labor to drive labor costs down by pretending there aren't people qualified to do the work.
After enough people couldn't be found locally they'd have a legal justification for a work visa.
Also, the notion that H1b's are cheap is not always true. With the added costs of filing H1b visa and green card, the true costs are much higher, especially in a cutting edge industry.
My question is why not spend that money developing smart local folks.
When it's not used for visa indentured servant games, it's arguably a relatively decent way to to do things (don't put applicants through a charade of being considered, and you're already certain who you want to hire), but better would be to not post the job at all in that situation.