Alienating a fraction of that workforce will impact them, I think.
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.