Heightens spectator interest. Pretty easy to see why some are included. Harder to figure why some are not.
Now, for all those people that you might be following, it's not just, oh, hell, why aren't they moving? It's also, go!, go!, get to the finish before your route turns orange! And when you refresh, a big sigh of relief when you see their route hasn't turned orange. Definitely one step closer to network coverage.

All in all, not a bad idea, imo. Easier to get my head around than the idea that if you cross any one of a multitude of thin lines, then you may as well be riding a bus, because you cease to exist for purposes of the "race".
Just a spectator. Wtf do I know?