It solves the issue of congestion the same way a band-aid solves the issue of an expanding bullet wound:
It doesn’t.
…but it’s a quick and dirty patch you can apply that makes you feel like you accomplished something while you never really put any thought into why you did what you did. It’s a product of democracy and compromise (with the two extremes being “let’s build transit! even if it might hurt us!” and “build nothing, save money, and keep the government’s hands off everything”) that pretty much does no one any favors.
Oh, I didn’t realize you were only talking about Amazon, specifically. In that case, yeah that’s probably true. But bigger trends also suggest it could’ve helped.