Between material-gathering, going to the work site, clearing the path ahead (largely avoided here by elevation, but still) and actually laying down the road one... block... at... a... time... roads are very slow to build in Minecraft. They take a large amount of investment before they start to pay off, unlike most buildings, and they can't really be fully appreciated except from map views like this site, so they're kind of low-reward for the people doing the work, too.

I only run a vanilla server, so I don't know how mods might affect that. Were these tool-assisted in some way? I just can't wrap my head around that time involved if not.