I too afk race but always do it on tranquil paths where I'm always matched with 7 NPCs (and if I'm not I just leave L1 pressed until race ends). Honestly if there's someone afking in say R160 sagolii, you can go to:

R160 Costa del Sol, R160 Tranquil Paths, R180 Sagolii, R180 Costa del Sol, R180 Tranquil Paths...

If it bothers you soooooooooo much, you have 5 other circuits, unless you are choosing "random"...which from my experience, always matches you in the circuit with real players, but if that's the case, it's your own fault.

As for this "reward" you speak of, there's really no reward. They give you what? Marginal MGP and chocobo exp? What do you even want that for xD? For a fenrir mount after afking in a million chocobo races? You can get the same amount of MGP in one day farming indolent imperial than in 1 month afking in chocobo races, complaining about how people are rewarded in afk racing is ridiculous.