Not my industry, but I wonder if building code requirements for contracted facilities construction has anything to do with this. Would be interesting to hear perspective of civil engineers on this, in particular, those involved with standing up fulfillment centers.
For example, a few observations from the 2017 Florida Building Code[1]:
Minimum 1 lavatory per 100 and 1 drinking fountain per 1,000 in occupancies classified for storage (per Table 2902.1). Natural inquiry that arises in my mind is what the specified occupancy of the fulfillment center in question is.
In occupancies other than malls, lavatories normally located not more than 1 story above/below the target space, path of travel not to exceed 500 feet (per 2902.3.2). However, there's a possible exception for factory and industrial occupancies which allow this requirement to be waived with approval. I wonder if Amazon has pursued this exemption when contracting the construction of their fulfillment centers.
[1] https://codes.iccsafe.org/content/FBC2017/chapter-29-plumbin...