"Algorithms". Even if your region has plenty of ad inventory, Google's micro-targeting can mean even people in the same household see wildly different subsets of the ad inventory. You could just be lucky and aren't in any of the micro-target "demographics" scams want (or at least, can afford) right now.

Micro-Targeting is one of the worst mistakes of the entire advertising industry and we'll be probably dealing with its consequences for a while to come.