Thanks for reading my piece!

I should preface this by saying I am not an economist or anything so these are just my personal thoughts. I agree with you that companies (mostly) act in their own self-interest. However, I think the objective of finding the best person for the job is not the only one. Companies also have the objective of maximizing their profits. Therefore, when looking through candidates for a job that is not at a senior level or highly specialized, among a number of candidates with approximately the same qualifications, hiring managers will most likely go with a candidate they expect will ask for a lower salary. As a consequence of this, I expect that flooding the queues would either push a lot of candidates from other regions out or worsen their power to negotiate wages and ultimately result in lower salaries.

Another factor is company culture and communication. I think (and again this is my personal opinion), if a majority of employees within a company or a certain department are from one particular country X, there is a higher chance they would pick a candidate from country X among a number of candidates with the same qualifications, most likely because they have a similar culture and can communicate better.