In most low-skill positions (especially the ones which favor physical labor over soft-skills), you are a body to be instrumentalized until you either leave leave or are disposed of. That's the reality of most work. Retention is as high as it needs to be to ensure continuous operations, and employee happiness is either incidental or primarily a slogan. The human element is made to be as irrelevant as the market will allow.
The Amazon Warehouse workers I've known have described it as warehouse work. Little better or worse in their experience than working at any other distribution center, though some centers are naturally likely to be ran more poorly than others.
I’ve talked with people who work there as engineers. I haven’t any friends there.
The engineers seem well looked after, but engineers are not what I’d describe as ‘low level employees’.
I’m not sure that rejection of unionisation says as much as you are attributing to it and if reports are to believe, Amazon used a few dirty tricks.
Likely both sides did, but there is plenty to suggest that Amazon isn’t a kind or benevolent employer.
To put it in perspective, there may be employees that hate working at Amazon, but there are also 100,000 employees. If only 10% of the employees hated working there, that's still 10,000 employees. But a 90% satisfaction rate for any company is amazingly high.