Alienating a fraction of that workforce will impact them, I think.
Amazon becomes their best available option, and once they work there for a year or two, improve their skills, get some experience, and get tired of dealing with hell that is working at Amazon, they get hired at all those companies they couldn't initially get into. No one says Amazon is incompetent at tech, quite the opposite. There is a lot people can learn while working there, and all those other competing tech giants know it.
I've heard of very few moves the other way around, and in every single such scenario I personally witnessed, there was a lot of very specific circumstances for the person that lead them to that point.
612k engineers. Let's assume that Amazon aims to hire the top 20% (I would expect software engineering skills to follow a power curve), so roughly 100k qualified workers.
That's pretty small if you're looking to employ 2-5k of them. That's a lot of competition given that there are likely at least 50 companies making Amazon-type offers.
I'm not saying they can't hire people if 10% of that pool decides they won't work there, but I'd imagine they would want to extend their pool to maybe top 30% at some point.
Amazon does a wide range of software development from robotics, backend AWS, internal software, and front end web development. So, most developers have relevant skills even if some positions are much harder to fill. That said their dev teams have many non programmers like systems administrators and testers etc so I suspect it’s closer to 2k US developers than 5k. As it looks like many of their openings are in Canada, Ireland, India, etc.