And, perhaps most importantly, Amazon derives no benefit from the length of a worker's commute while Amazon derives all of the benefit of employee security (really, theft) screening.

A better analogy might be employees changing into a required uniform, which (I believe) is also exempted, though obviously does not typically take ~25 minutes every day.

I think you are on the right track. Further amazon is incentivized to save money on security staff even if it costs employees cumulatively hundreds of hours of work since employees wait time is free and individual employees are very replaceable.