The cynic in me thinks they are concerned less with this disproportionally impacting people of color and more with wanting to be the preeminent distributor of marijuana.
I'd say more they want to be able to hire a ton more people at their distribution warehouses (without being excluded for insurance, drug testing, liability, etc)
I'm cynical too, though I frame Amazon's motivation somewhat differently: what low-cost political positions can I vocally support to placate the party that would normally support workers and oppose corporate power?