| Because supply is influenced by price. The supply of gold is huge if I am willing to pay above market rates. If I want a conductive metal I am going to chose something other than gold in the vast majority of cases because of price. In the case of gold the price is based on both demand and resource extraction costs. Moving to the workforce, students pick jobs in part because of what they will pay. Over time this feedback loop combines with demand and other factors to set a clearing price for the industry. If a job pays less than 100k that's a very big sign that people are choosing to do something else because of pay not the jobs inherent difficulties. Now what happens if you try and subsidize an industry with H1B's. Let's say you add 50% as many H1B as people working in the field for a huge effect. Well in the short term wages fall and people either find something else, but more importantly students study something else. Fast forward 20 years, the market price is a little lower but not by that much even though lots of H1B's are now doing that job' you still need to entice a lot of US workers. Meanwhile close to 1:1 with those H1B's, US students have moved into other fields. Thus, unless you are going to have most people in an industry be H1B's trying to help out an industry shortfall with some H1B quota is not that useful and simply subsidizes an industry for minimal benefit. PS: Even defining things based on job is tricky. I need a Doctor what's the price for that, type: surgeon, type of surgeon: cosmetic. Now a hospital that can fill out generalist one level up can get a discount. Even industry gets tricky as a school may need a doctor for example. |
You can't explain things based on an entire economy without taking into account the entire economy, and all it's parts and interactions; much like, say, blood-sugar levels in the body involve multiple organs.
If you focus on one area of the economy, you must avoid those 'non-local' attributes, unless you are willing to do this. If you analyse the attributes of any local economic part enough, you will eventually hit upon a non-local attribute; Hence, any analysis eventually hits this roadblock.
Back to context, the specific effect of H1B visas, on national salary is complicated, because salary not only is non-local, but involves the silent interactions of supply vs demand across and outside the nation. You'll hit all sorts of GM-like fallacies if your analysis is too shallow.
This is why it is necessary to take it, almost as 'faith', in the mechanics of the market; A true analysis of market principles is a complex process indeed, most people can only take them on faith at some level. Even mathematicians accept some (personally) unchecked axioms.
[1] https://en.wikipedia.org/wiki/Parable_of_the_broken_window