Maybe you're familiar with the Federalist Papers written by James Madison, Alexander Hamilton and John Jay. Federalist Number 68 concerns "The Mode of Selecting the President."
Federalist No. 68 explains why such an important function (choosing a President) was delegated to a small number of very important persons (electors):
"It was equally desirable, that the immediate election should be made by men (the electors) most capable of analyzing the qualities adapted to the station, and acting under circumstances favorable to deliberation, and to a judicious combination of all the reasons and inducements which were proper to govern their choice. A small number of persons, selected by their fellow-citizens from the general mass, will be most likely to possess the information and discernment requisite to such complicated investigations."
Obviously, the Founding Fathers thought that choosing a president required "complicated investigations" and that the selection of a president should be made by people "most capable of analyzing the qualities adapted to the station, and acting under circumstances favorable to deliberation, and to a judicious combination of all the reasons and inducements which were proper to govern their choice."
The Founding Fathers saw the job of an elector as being much more than the perfunctory, ministerial function that you envision for them.
The 12th amendment states in part:
The Electors shall meet in their respective states, and vote by ballot for President and Vice-President [] they shall name in their ballots the person voted for as President, and in distinct ballots the person voted for as Vice-President, and they shall make distinct lists of all persons voted for as President, and of all persons voted for as Vice—President, and the number of votes for each, which lists they shall sign and certify, and transmit sealed to the seat of the government of the United States, directed to the President of the Senate; the President of the Senate shall, in presence of the Senate and House of Representatives, open all the certificates and the votes shall then be counted.
They vote. Nowhere is there mentioned any other function or grant of authority. Electors are assembled for this one purpose and then disbanded.