They will lose their most expensive employees who have the most economic security such that they can quit or find other jobs.

Under capitalism, proletarian wage labor is a commodity, this makes its cost minimizable. Tech workers have been spared some of this due to petty bourgeous aspects of their economic relations, part of which was just that they were in short supply and could demand upwardly mobile career paths plus the fact that your direct work really just requires a laptop. Amazon would like its employees to be proletarianized, to be more precarious, to be replaceable, so that they can pay them less and have greater capacity to discipline them. This is also why there was and is a large push for "STEM" education by the FAANGs. Their "labor shortage" arguments are really just a reframing of "we wish we could pay you less and treat you worse by increasing the size of your labor pool".