The people are allowed to vote in the Colorado caucus. Here you can find the rules on how they can.
http://www.sos.state.co.us/pubs/elections/Candidates/FAQs/caucuses.html
Take a look and you will see how little it takes. If Trump would stop bragging about how little he had spent and actually built a ground game he may have picked up some delegates in Colorado.
Trump did not show up for the contest, but he still thinks he deserves to win. Leftists believe they are metaphysically superior.
So why have voter primaries, just call them delegate primaries and let them have delegate rallies, just forget about what the people actually want, just the delegates matter. Glad Trump is exposing the absolute corruption of the political process and Cruz is indirectly helping too by just playing the game the corrupt way it's set up to be played.