The idea of our democracy is that the will of the people prevail since the ones in office want to be voted in. The problem is that it is a very slow process. Usually you have very few choices and you pick your battles. Although there is a right and left amongst politicians, there is a common ground, as well — they are all politicians. Their interests are not necessarily ours.
A senator won’t care much about the will of the people in his state if he doesn’t have to answer to them. He doesn’t have to worry much about the worries of the state legislators since they (the legislators) won’t be voted in or out based on who they appointed as senator.