We can simply calculate each states electorates and see who wins. It just mean the relative power of each state. There is no reason to let real people gather and vote. Why not change the amendment?
Why were real Electors historically chosen?
The Founders' original intention was for the Electoral College to consist of people that were better educated than the average citizen. From The Federalist Papers, Number 68 (emphasis mine):
It was equally desirable, that the immediate election should be made by men 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.
The same paper also stated that an Electoral College was desirable to prevent an unqualified candidate from winning.
The process of election affords a moral certainty, that the office of President will never fall to the lot of any man who is not in an eminent degree endowed with the requisite qualifications.
Additionally, by having Electoral Colleges be per-state, Hamilton believed that a person who relied solely on "the little arts of popularity" could be influential in a state, but would ultimately be thwarted at the national level due to the education of the electors?
Talents for low intrigue, and the little arts of popularity, may alone suffice to elevate a man to the first honors in a single State; but it will require other talents, and a different kind of merit, to establish him in the esteem and confidence of the whole Union[…]
If Electors today almost always vote for their state's popular vote, why keep them around?
Partly, it's a historical legacy. However, there are a couple of reasons why this is still kept:
- If a candidate were incapacitated or killed before the Electoral College votes (on the Monday after the second Wednesday in December), the Electors can choose an alternative candidate. This happened in the 1872 election when Horace Greely died before the Electors cast their ballots.
- If a patently unsuitable candidate won a state's popular vote, an Elector could vote for a different candidate if their state allows them to. Before dying, Horace Greely was committed to an asylum. Had he still been living at the time of the Electoral College vote, the Electors would have been permitted to choose an alternative candidate. Note that in the 2016 election, there are Electors who have publicly stated that they will vote against Donald Trump and vote against Hillary Clinton because they believe them to be unfit to be President.
In case you are wondering, a running mate does not become Vice President until the Electoral College votes. So if a presidential candidate dies before the Electoral College votes, the running mate does not automatically become President (unless the Electors choose to vote for them).
Generally, the reason real people are kept around for the Electoral College is to handle those "what if" situations. Rather than codifying every possibility, real people can make a decision to handle whatever happens.