That's because state politicians stick it to interstate truckers because they can't vote. Buy a diesel car, pay more taxes.
Buy a diesel truck, move out of state...................
My guess is, with the way the International Fuel Tax Agreement (IFTA) works, is that truckers who drive into, or through Illinois, and fuel up there, are getting a net refund from Illinois on fuel taxes every quarter. Of course, that net refund will go to pay taxes in another jurisdiction.
For those not familiar with IFTA, the way it works is to allow interstate truckers to deal with (mostly diesel) fuel taxes for all the lower 48 states, and 10 Canadian provinces, with a single quarterly filing in your home jurisdiction (state or province). With diesel for interstate trucking, you only owe taxes on the fuel you consume in that state/province.
Example, say you drive 500 miles through three states, but you only fuel up in the last state (say 100 gallons for a net of 5 miles-per-gallon).
State A has a $0.23/gallon tax rate, state B has a $0.20/gallon tax rate, and state C has a $0.25/gallon tax rate. You drive 100 miles in state A, 250 miles in state B, and 150 miles in state C. So, you initially paid state C $25.00 in fuel taxes on that 100 gallons, but you only consumed 30 gallons there.
So on your quarterly IFTA return, you fill out that you drove a total of 500 miles, and consumed a total of 100 gallons, for a fleet average MPG of 5.0.
You drove 100 miles in state A for a taxable use of 20 gallons at $0.23/gallon, so you owe state A $4.60 in fuel taxes.
You drove 250 miles in state B for a taxable use of 50 gallons at $0.20/gallon, so you owe state B $10.00 in fuel taxes.
You drove 150 miles in state C for a taxable use of 30 gallons at $0.25/gallon, so you owe state C $7.50 in fuel taxes, but you paid state C that initial $25.00 at the pump, so you get to net the $7.50 due against the $25.00 paid, for a refund of $17.50 from state C.
So, out of that $17.50, you pay state A and C (all netted on the form) the taxes due them (a total of $14.60). Then, at the bottom of the form, you net all the taxes due against the all the taxes paid (due $22.10) and all the taxes paid ($25.00) and get a total due or refund. In this case, you'll get $2.90 back.
The forms get sent, electronically, to the IFTA clearing house for all jurisdictional taxes due/paid, and the jurisdictions settle these taxes amongst themselves based on the filed returns. You only pay the net due to, or get the net refund paid to you by, your home jurisdiction.
I well remember when Blajoavitch first took office, he proposed a special tax on in state trucking companies. A group of owners got an audience with him and let him know just how mobile their business was and promised him that they would set up operations in neighboring states, if he pursued that "special" tax on them. He quietly dropped his efforts.