Tax expenditures are funny, They're not taxes, exactly, because they save us money. They're not spending, exactly, because the dollars are never actually spent. They're somewhere in between. So think of it as tax spending.
Or just think of it as the ultimate nudge. The carrot hiding behind the tax code's big stick, tax spending guides us by making certain behaviors and actions cheaper. We encourage employers to provide health care by taxing wages and not taxing health benefits. We encourage investing by making a dollar earned from dividends cheaper than a dollar earned from a salary.