I think they do it because they are risk averse, and politicians give in easily to peer pressure and popular pressure, especially that "popular" pressure whipped up by the media, and most people make a false analogy between personal debt and government debt, and therefore there is the sense that government shouldn't run debts because normal people shouldn't run debts. I doubt a class interest can be involved because in a deep recession the business class has as much interest in seeing the economy stimulated as anyone else. The fact that the business class often used to come out against stimulus suggests they were stupid, since a lack of stimulus merely decreased their profits.