The bottom line in this Opinion Journal story is that while the Republicans cast their vote with a slip of paper, the Democrats have a mind-numbingly complex system in which participants divide up into "candidate preference groups" by standing up. No paper ballots are used. Those candidates who don't get support from 15% or more of those attending a local caucus are deemed not to be "viable," and their supporters have to realign with some other candidate.
Further, for the Democrats, the state party can bend the rules as described in the article so influence can directly result from who has the best organization/spends the most money. That may mean Hillary...
There’s a reason why systems are sometimes made complex and confusing, and it’s not to obtain an honest, straight forward outcome.