Casting votes by state forces candidates to be attentive to local interests, which they would otherwise ignore in a national campaign.  The electoral college is helping promote democracy through implementing a mechanism that make candidates pay attention to local issues, and actually do what they are elected to do- serve the interests of their constituents.  A presidential candidate is of course going to focus on a more national level interest, but in order to visit and campaign across the country, the candidate must be at least aware of the issues that of particular interest to the local area.