I'm an SDE II at Amazon. Posting because I hope other SDEs read this; there is strength in voices.
I absolutely will join a strike if Amazon lays off unionizing unskilled workers en masse.
The pay is good, but I think you're missing two things.
(1) A large portion of Amazon SDEs leave after a year or two anyway. (The lack of vested RSUs in the first two years is typically compensated with an equivalent sign-on bonus, which pays out with each paycheck. So the vesting schedule doesn't particularly incentivize sticking around for no other reason.)
(2) Many Amazon SDEs (like that of any FAANG) are millenials, who skew progressive: worker rights are an issue I think many feel strongly about, and many probably have friends who are part of the unskilled labor pool or gig economy. We know if it weren't for software, we'd very well be in the same boat.