Why is it important for presidential candidate to spend more time campaigning in states with a higher population than lower population?

The larger state, the more votes. If the state has a large population the state have more votes to give. The states vote as blocks. So if 51% of people vote for a candidate in a state it is if 100% votes for that candidate. 9 states in America have nearly 60% of the US population. So without this system the whole race would only involve only those 9, and within those 9 only the massive cities they have. Ex. Chicago, New York, LA etc.