Some people don't want the government keeping track of what they're doing, unless the government has reason to believe they're doing something illegal. This sentiment is so strong to Americans that it is expressly stated as a reason for rebelling against British rule. Taxing consumables allows per-distance taxing without the tracking that comes from toll roads or mileage tracking.

Also, lots of publicly funded transportation infrastructure fees don't closely track usage. Many popular public transit systems charge a single fee for unlimited continuous usage or charge per day/month. There's other weird quirks, for example when going the San Francisco Bay area, I always plan my stops in a clockwise direction, because then I don't have to pay bridge tolls when traveling in that direction (north and east), but would in the opposite direction (south and west).