I don't think it's so much about whether or not they're minorities so much as it's about those particular areas having very low demand for services that cost more, thus they can't take advantage of economies of scale.
I don't think this has as much to do with economies of scale because the way in which deliveries are routed can be optimized if there are only a few deliveries in a low-demand zone.
The reasons cities want equal access for low-income areas are many and they include, for sure, non-discriminatory access. But they also include the preservation of future urban revitalization (aka gentrification). If highly-moblie affluent residents choose where to live based on amenities such as walkability, entertainment, restaurants, parking, cleaning services, etc, you can bet that same-day Amazon delivery will be one of those amenities.
If same-day Amazon delivery is not available in an area, it will be one more reason an affluent resident will not choose to live an a neighborhood despite that it may be more affordable in terms of rent which in turn would me revitalization efforts would be stymied.
So far, there are dozens of comments expressing confusion and anger that poorer neighborhoods would be guaranteed the availability of same-day delivery and much of that confusion and anger seem to signal race as problem (e.g. snide references to "SJW"s). To my mind, the issues of class and race have people so inflamed they cannot see that arguments that deprive citizens of access, for whatever reason, are actually bad for the economy, period.
Members of the socioeconomic middle class are not having a rough time because the Federal government is taking all their money and doling it out to poor people. They are having a rough time because they are shouldering the economic burden that the wealthy have shirked.
One day, all members of the middle class may realize that depriving the poor access to good actually accelerates rather than retards the economic disenfranchisement of the middle class. But given that the leveraging of racist and xenophobic sentiment by elites to pit the middle class agains the ranks of the poor, such a realization seems distant at best.
More likely, much of the middle class will continue to rage against the poor, arguing that the poor should be allowed to suffer and that the poor don't deserve access to the benefits of modern civilization. Unfortunately, these members of the middle class may all too soon find themselves among the ranks of the poor and disenfranchised and they may wonder why they deserve to suffer so and why they do not have access to the benefits of modern civilization all around them.