Jet Fuel Tax Refund

I am perplexed by the IRS' claims that Jet Fuel is getting diverted for
highway usage.

Isn't Jet Fuel more expensive than diesel wholesale? I know it is more
retail. It just doesn't seem logical that people would be buying Jet to
avoid the measly difference in taxation. After all, most won't many diesel
engines wear out on Jet A if you don't add lubricants to it?

Does anyone know anything about this? My guesses

A: Some number cruncher found discovered a discrepancy in the Jet A sold and
the Jet A used numbers and can't figure out the discrepancy so they assume
cheating.

B: They have real evidence, and I am missing something.

C: They want to float the difference on the refund to make some budget
money.