Or, the poll is skewed because of an unbalanced sample population. The methods of the poll are usually not very scientific and it is designed to get a specific result. Now, there are accurate polls. But these polls are used by the politicians to gauge the sentiments and beliefs of the populace so that they know precisely what to tell them. Politics is down to a science now.
Polls help the political class to scientifically pander to the voters.
Political campaign propaganda is a specialization of the science of modern propaganda.