They really aren't. Each state has different rules for getting on the ballot, and there isn't a lot of wiggle room on them. Most are in the form of "$x% signatures of $y criteria". For instance, 5% of the number that voted in the last gubernatorial election. Plus some paperwork and the like. Third party candidates have trouble meeting these requirements.
The only thing here is that the Democrats are claimed to be watching these efforts to ensure that other parties are following these rules. They'll be watching Republican candidates as well, but that's unlikely to have any effect.
I would love a different system, such as RCV, but this is the system we have. You can probably start a petition to create it in your state, but the process varies wildly.