To be fair, it doesn't seem like the developers could/should be installing sidewalks on land that isn't theirs without coordination with the landowner (so they have to end the sidewalk at the edge of their land).
That makes sense and is how it's typically done up here. I read the GGP's post as a complaint against the developers not against the city/country/AHJ, who is the only one in a position to make the change (granting public right of way, or taking property via eminent domain as needed).
It was meant as a complaint against the county. They have a silly rule in place - developer must build sidewalks. That's it. No coordination between developers/land-owners. No plan to link developments. See the sibling comment about Loudoun Station - a large mixed-use development that isn't linked to the largest bike trail in northern VA.
