It is a simple answer ... vehicle tires wear as a result of compound, design, weight, driving style, and air pressure (there are more but these are the most common reasons). Because a vehicle tire goes typically at a higher speed more heat is generated. Add in the road condition (abrasiveness of the road surface to name one) the loaded weight of the vehicle and the tire will (it takes a high speed camera to pick it up) what is called jounce. That is when the sidewall flexs. Every time it flexs that movement generates heat. Then if as most people drive throw it into the cloverleaf at speeds higher then posted (most people drive according to their seat of the pants). All this adds up to tire wear. On a bike you don't experience the high speeds nor the jounce. Bike tires don't have as much tread depth as compared to passenger tires. (most passenger tires depending on the make/model and size vary from 9 - 11 /32nds of tread. The cheaper the tire the less the tread depth when new.) There are other factors but I don't want to write war and peace!