The DOT has all 50 states over a barrel in this way. States must either do what the fed wants or be denied DOT funds.
Illinois contested a motorcycle helmet provision for three years, the money was put in escrow. The helmet reg. was finally pulled and all the dough was freed up. This was about a dozen years ago. We had a different state government then.
He gets regularly lambasted in these threads by people who don't like DUI regs.