Our nation is a federated union of distinct states – each of which has a different perspective on how the federal government should work. Profound state differences have existed since before the founding of the union. Accordingly, the Federal Constitution (CotUS) preserves both the will of the people AND the will of each state when electing leaders to the Legislative and Executive branches of the federal government.
The legislative branch includes two major bodies: the House and the Senate. Each representative in the House works (at least in theory) on behalf of constituents in a single district within a single state. Districts are defined by population. This means the more populated states will have more districts and thus a proportionally stronger representation in the House. The House, in this regard, provides popular representation for the people. The senate, in contrast, is designed to represent the states themselves. Each state, regardless of population, has two senators - two votes. By constitutional design, the Legislative branch (congress) represents the will of the people AND the will of the states. And, consistently, the same is true for the Executive branch.
The executive branch has only two elected officials: the President and the vice-President. Individual voters express their will by voting for their desired candidates. But as with the Legislative branch, the will of the people AND the will of the states play a role.
Voters in each state determine how the electoral power of their state will be applied to the candidates. The voters determine who they want their state to 'vote' for; these state votes are called electoral votes. As with the Legislative branch, the more populated states have more electoral votes and thus have more influence on who is elected PotUS. The mechanism that achieves this balance is known as the electoral college.
The electoral college was designed to enable BOTH individual voters AND individual states to select the President (and vice-President) of the United States. The electoral college is a collection of human electors each of which is caretaker for one electoral vote. Each state is granted one elector for each Legislative branch representative – one elector for each senator and one elector for each district (or House representative). In result, the electoral college apportions power among the states in elections of the Executive branch† consistent with the apportionment used to elect members of the Legislative branch.
Our founders believed that each state should have a meaningful say in the business of the federal government. They designed the CotUS so that federal elections are based upon the votes of the individual people through a lens of federated states.
The Executive branch, in particular, caters to the entire nation of individuals AND the entire federation of states. With the electoral college system, voters determine how their state will direct its electoral power and the electoral power of a state is a function of its population. Thus larger states have more influence (as states) but cannot effectively nullify the wishes of smaller states. For example, millions of surplus votes in California or Texas not only convey massive electoral power of the state to their chosen candidate, but could easily reverse the sometimes dramatically smaller margins in other states. A national popular vote would perfectly preserve the will of the individual people but at the expense of the will of the states. The founders did not want the states to lose influence and the system they devised to achieve this seems very logical and consistent.
Those who wish to do away with the electoral college ipso facto believe that the states should not have any influence in Executive branch elections. The founders saw things differently.
† Electors are actual human beings who are supposed to vote according to the will of the people via the popular vote. They almost always follow this tradition and those few who have voted against the will of the people have never affected the outcome of an election. The use of human electors is, in my opinion, pointless nowadays and should be eliminated by simply mandating electoral votes actually match the popular results within the state.