US has unfortunately been union-unfriendly since Reagan.
This got further cemented when the USSR was formed, and it actively supported many left winged militant organisations in europe. This was used as leverage by trade unionists and social-democrats to demand further rights (or else the militant forces will get into power and things will end much worse for the establishment).
This dynamic only really changed right before world war 2, when stalin (and other USSR leaders) focused on a policy of "socialism in one country" instead of a the dogma of a worldwide workers revolution.
I bet they’ve done all kinds of risk calculations around increasing benefits and decided they could stop there. Personally, I hope their calculations are wrong and the workers unionize anyways.
Amazon warehouse jobs are physically demanding and damaging (which should carry a premium) and extremely optimized to negative downtime (which should carry a premium). (Employees are required to do work while off the clock, walking between work area and break area, and waiting in line for security checks).
The government can lower the supply of labor willing to work for low wages by offering a basic income, pay for people’s education, etc.
The government can increase the demand for labor by decreasing the number of hours needed to reach overtime (per day and per week), mandating vacation time and parental leave, etc.
All of this, however, very explicitly increases government expenditures requiring tax increases and clearly shows the wealth transfer, so it’s politically less popular than trying to foist it onto select businesses.
There is a push to raise federal minimum wage to match Amazon's minimum wage, but for now they are paying a hefty premium everywhere in the US except Washington D.C., the only US state-like entity to yet match it.
Sometimes we forget that all these amazon warehouse employees could take jobs as cashiers at slow stores and similar such easier opportunities, but choose not to.
With Amazon's massive investment in robotics and other opportunities for automation, they think they can become exponentially more efficient. At that point, a non-unionized workforce will lose that goodwill and be slashed into a fraction of its current size.
In an ideal world unions shouldn't have to be anti-automation, because people should have access to other sources of income (yes I mean income, not specifically employment) if they lose their jobs. This way we aren't holding back technological progress to protect people from poverty.
I have no idea what that ideal world looks like, maybe it's not possible. But I do feel uncomfortable with the idea that automation is somehow inherently anti-worker with no opportunity for reconciliation.