The incentives to married couples are probably less than if they were single and filed separately. This is definitely true of two working spouses as both incom

The incentives to married couples are probably less than if they were single and filed separately. This is definitely true of two working spouses as both incomes would start from zero. For one spouse staying at home, they would now qualify for all forms of assistance and tax credits. Balance that against the single earner's reduced break points on marginal taxes and the status quo probably brings in more money to the government. Of course it looks like big incentives when you don't look at the penalties from being married.