I've always assumed that the so-called "talent shortage" was an excuse to get cheap labor from abroad. They make job ads such that it's improbable that a local will meet the highly specific requirements, after which they complain of a skills shortage, and then they have their excuse to import cheap labor.
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.
I actually recently spoke to somebody who said his job was to exactly this. He said they'd find a remote candidate, with random skills X, Y, Z, and his company would then craft a very specific job opening that could only ever match this particular employee.
After enough people couldn't be found locally they'd have a legal justification for a work visa.
Did you ever imagine if both ends of the spectrum are true? Maybe there is a talent shortage and maybe there are companies trying to get cheap labor from abroad. We are a reasonable sized company trying to recruit people with advanced skills. Finding talent that includes large number of H1B's is hard on its own. Forget finding talent that excludes 95% of the world (aka H1B's). Most of the candidates I get to interview are usually immigrants. Why? I don't know. We have zero motivation to hire immigrants specifically. We pay way higher than an average company and are more interested in talented candidates than saving money. It's just that immigrants are the ones with the skills that we need.
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.
This isn't specific to justifying a visa. This same method is sometimes used when the obvious choice non-cheap-labor hire has already been picked by the hiring manager, but they're required (for any of a variety of reasons outside the manager's control) to post the job.
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.
