It's solely to surpress wages.
That being said if you honestly believe there is wage suppression then I recommend programming outside of office hours and getting as much practice as possible so that you can rise to a senior position where such problems are absent.
I didn't say it had anything to do with immigration. But it does have to do with suppressing wages, which is what they comment you were replying to was suggesting as a motive. My point being that tech companies have a history of this.