I think your information is wrong. That GOP website says that any registered Republican can vote at their caucus for delegates. But we all know that Cruz STOLE those delegates. /s (At one point I could post on FR without the /S. Nowadays.....)
The people in Wyoming, CO, etc. are in charge of their state’s delegate selection, party activities etc. Most people don’t make the effort but they do have a voice or a vote, if they choose to stay on top of it before the train leaves the station.
It’s just easier to get on here afterward and bray that they wuz robbed or cheated than it is to do the hard boring work in the trenches.