Because they are the policy least objectionable to those outside the party. And because tax cuts are an affirmation of faith to conservatives. Don't give tax cuts to the rich. But outside the GOP, tax cuts aren't selling. The Cold War is over.
Crime is down.
The economy is good. Republicans are split over abortion and gay rights. Republicans don't have any agenda. That's why liberals are driving the agenda in this campaign. For the first time in 40 years, hard-line conservatives have no serious contender.