Why not rural areas first? The average trip is probably more miles and less complex roads, e.g., single lane in each direction and fewer interactions. I suppose there could be concerns of overall utilization and "wasted" miles/time picking up, but those probably affect profitability rather than desired utility. And even then, the current baseline for some people could be to not take a trip, so even if there's an extended wait, that could be better than say waiting until the weekend to get groceries.