Because people vote for the politicians in power. If they want to get re-elected, they need to follow what their voters want. At least, that's the idea. Plus, i

Because people vote for the politicians in power. If they want to get re-elected, they need to follow what their voters want. At least, that's the idea. Plus, it adds shame to the politician if he supports something that his constituents hate. For people filled with the pride of being a politician, some good old-fashioned shame could work wonders.