You can only vote for the governor of your state, not another state.
That is the point - just as a vote for governor is a state election a vote for president is also a state election because you are not voting for a candidate you are voting for a slate of electors who have been given power by the state to choose a president.
So accumulating those votes by political party to come up with a national total makes just as much sense as accumulating all of the votes for governor by political party, because just as with the election for governors,
these are also state elections not one national election.