Speaking as someone who lives adjacent to Bessemer but who does not work at Amazon, you need to understand that Bessemer is a dying city, a slum. These were the best paying jobs that many of these workers had had in their entire lives, it is no wonder that a majority of them decided not to bite the hand that was feeding them.
I was a union member back in the last 1980s through 1990s early. I was in a low skilled job where we paid our dues and got exactly nothing for it. Oh we had a wonderful contract that specified it all. It was great for basically keeping anyone new boxed in. Each quarter if we were lucky we got a visit by our local union rep in her Mercedes which cost more than many of us made a year. So I am so not a big union supporter and lean against them.
On another personal note, they spent decades harassing my uncles, now cousins industrial roofing business calling OSHA and other inspectors out to where even the OSHA representatives joked about it. It became a coffee break for them. All this over a company with less than thirty people at max.
So while they may have some application on higher paid jobs when you are low wage there isn't much they do for you other than suck two hours of wages or more from you each month.
People here glorify unions have no experience with them at the level that would have been seen in Amazon. They have these grandiose ideas how everyone benefits. Oh don't get me wrong, you are likely to get some changes that are beneficial, but in the end you are still exactly where you are before but now its all in nice pretty print writing which spells out exactly how you aren't going anywhere fast. Oh, don't forget the monthly payout (could be weekly in some places) and don't expect much if you ever actually reach strike stage.