The problem isn't so simple. If throwing money could solve the problem, it would have already been solved. The problem is that laying sewers or installing water supplies involved dealing with the local population and make them understand why it is important that the roads are dug and the sewers installed. Why should the population spend money to connect their house to the sewer?

Also, this takes planning at the city level because, once laid, the sewer needs to connected to a larger pipes so that the waste may be transferred somewhere else. Now, people living in the other area need to be convinced that their fellow humans need the sewers and their roads should be dug up.

The roads being dug up is a placeholder for infrastructure work related to installing pipes. As long as people don't see it as a serious problem, they will try to avoid the inconvenience of installing sewers.

This is just the cynic in me, but sometimes I think politicians let it be a problem so that they can use it in the next election season.