The parties emulated the electoral system within the States.
The delegates are analogous to the electors but, the parties are non governmental and can set up any mechanism to define their “electors” they choose, much as the States can. They can hold primaries, conventions or sleep-overs if they desire. Trump chose to run as a republican (though he has supported democrats and their policies many times) because third party candidates have not been terribly successful in the past. Now he says, I made it to third base and should just be given credit for a home run.
No, apparently most did not. Otherwise, a vote for citizens’ input would have been held in Colorado. Don’t even try to claim it is the equivalent of the Electoral College.