It's easier to crack down on the cheat who defrauds the country of £1,000 than it is to crack down on the multinational corporation that defrauds the country of £billions.
It's not exactly cracking down on them either and would make it potentially harder for them to earn money. In addition, I'm not sure it will stop many from driving which then just adds to the problem. As aruntraveller covers, populist bullshit