Why cannot there be several energy sources and consumers in different places in a DC network?
Your schematic isn't a grid. Things get complicated as soon you have multiple possible paths between power stations and loads.

To avoid overloading of the direct paths, you have to be able to adjust the load distribution. In AC networks quadrature boosters are the measure of choice.

These are just transformers, they are available for all voltages, relatively cheap, need very little service and can easily be installed in an outdoor switchboard plant.

To achieve the same with DC, you need a UPFC, which is a costly electronic device and needs lots of transformers and circuitry around it. And a building. When you see the bill, you stick to AC.