What factors contributed to the presidential selection system we use today?

The concern over succession

The founding fathers assumed that the average citizen would not be educated and qualified to understand the legalities, procedures and issues involved in running a country and dealing with other nations. They also did not trust congress to have the power to vote and decide who is a president. The plan was to have the population in each state vote for a group of intelligent educated people who would understand these matters. These people would than gather together and determine which candidate was best qualified to run the country. This process was called the electoral college. It did not actually wind up happening this way.