With no rapid mass communication, there was no way for potential presidents to reach all the people. Electors were chosen based on their ability to represent the basic desires of those who sent them to the capitol, but those senders were usually state legislatures, not the mass electorate. Because of the inability to communicate from the capitol to those legislature, they were expected to exercise their best judgement.

One day maybe we'll get around to a direct popular vote for president, but we've got bigger problems in the process than that one.