They do by the electors awarded to each state based on population. California has far more than South Dakota has yet South Dakota still has a say with their electors because it kind of balances it out.
This means that a candidate can win the bigger states but still lose if the smaller states vote against him.
It's a brilliant system actually.
There is also another factor to consider.
If we had a popular vote then politicians would spend all their time and money in the most populous states, they would have no reason to ever visit South Dakota meaning that the citizens of small states would not get their specific issues heard.
A candidate isn't going to care what issues are going on in a small state, they will only care about the issues in the bigger states because they need the votes.
People in South Dakota have far different issues then people in California do.