Caucuses are a problem when you are trying to rig the vote. People/voters know how many bodies voted in each precinct so lying is not possible.

They need candidates to stay in so they can justify splitting the delegates and making sure a brokered convention happens.

It would be hard to claim some candidates should stay in when voters can see with their own eyes the number of people for that candidate was small or nothing.

If it were only 2 or 3 candidates, Bernie would take enough delegates

https://www.washingtonpost.com/politics/campaigns-warn-of-chaos-ahead-of-the-nevada-caucuses/2020/02/16/ef78ef52-50c8-11ea-929a-64efa7482a77_story.html