I assume it isn't a logic issue, more likely a logistical issue.
I should add that Amazon did this with Amazon locker as well. Northern VA got coverage well before DC. My suspicion is some kind of incentive that VA is providing to Amazon, the same one that attracted Amazon to build its huge us-east data center in VA.
I was going to suggest that No VA is more affluent than DC, but in that case they shouldn't be in Baltimore.