The RNC is a private organization. It can do what it wants. The lawsuits have failed before.
Failed to do what?
Lawsuits aren't needed, simply that the people who make up a political party in a state demand that the selection of delegates reflect the will of the voters and not the will of a small number of party insiders and activists.
This election has been a lesson in how these things are done in various states, and people don't like what they've learned.
Private businesses and organizations get sued all the time for fraud. “Those are the rules” that we wrote doesn’t cut it. There are class action lawsuits all the time.
Candidates and donors spend millions of dollars to win a primary and delegates and the party can change the results after the vote.
That is clearly fraud.