That is what they do. But then they want to know why the secular schools get so much more of their tax dollars than the parochial schools they want their kids to attend.
If parochial schools are businesses then school vouchers are sending retirees social security checks rather than operating state-run homes for the elderly. It allows people to buy what they want in the market (from businesses) instead of being restricted to a choice between a government facility and nothing -- not even a refund of the tax dollars not needed to pay for it when you don't use it.