It's because they always do the businesses before residences. So it depends on the type of area.
If bus/res are interspersed, vs a business center of town and residences outside vs a rural area, they will have a different delivery strategy.

Where I live they "double back" and do the residences last. In a more rural area they can't afford to do that and do things more geographically in order.

... or something like that...