In part because the idiots who opposed it bought bigger shiny new trucks they'll never use for purpose. Filled up their extra large tanks and burned as much fuel as they could in spite.
Vehicle taxes should be based on weight and square-footage between the bumpers. All of a sudden a compact pickup gets taxed like a minivan and the Ram 23,000: Spousal Abuse Edition, with the same size box, gets taxed like a tank. This also evens the playing field a bit with ridiculous EVs like the Cybertruck (3 tons) and Hummer (4 tons) that put extra wear on the road. (For comparison an Ioniq 5 SUV only weighs 2 tons)