While it's a far cry from 1,400x more in fuel tax, semis do get "punished" for their poor fuel mileage (paying more tax per mile driven) compared to a person in a Prius. In Iowa, the tax is 30.8 cents/gallon for gasoline and 32.5 cents/gallon for diesel. [1] At 53 mpg and 6 mpg, the tax cost per miles is 0.616 cents and 5.42 cents respectively. And of course electric vehicles avoid this tax entirely.
Applying the tax on a per-gallon basis is great for environmentalism, as it encourages higher fuel efficiency. Applying it by vehicle classification and cost/mile could eliminate the subsidization, but would be a huge pain to keep track of.
[1] https://tax.iowa.gov/iowa-fuel-tax-rate-changes-effective-ju...