They actually have many options, no way Amazon is the only employer that would employ them, and they chose Amazon probably because it’s actually the least evil of options or somewhat “better” in something. It doesn’t have to be actually better in terms of work or pay etc. but perhaps how easy it was to commute (though I heard Amazon has plenty of work benefits actually)
Now other employers have to compete because they need an employee too. So they try to one up Amazon. If they get good enough Amazon will lose too many employees and have to one up the other employers. etc.

Ok but this clearly doesn’t seem to work well, right? Wages stagnating and harsh work etc. This is probably related to many factors but I guess job security is a big one, people don’t job hop as much and fear getting fired homeslessness etc. Another one is too many potential employees to choose for limited spots (with the increasing levels of automation in every kind of work), so much that employers can actually down on their work conditions and say “ok then, whoever can stand these conditions for this price can work here”.

I’m not some economist or something but I believe UBI or some derivative of it at least would be the leverage for that. If someone who just got fired were to receive 1000$ per months on top of their current savings for 24 months, they won’t be so much of a risk and won’t be inclined to work in a 1200$ per month job either. We don’t actually need this constant race of upping minimum wage and many other band aid regulations if that could be a thing.