They know if President Trump is on the ballot there will be unprecedented energy in the MAGA movement. A positive energy that will in turn attract more and more people.
So many people that rigging the election will be so many magnitudes more implausible than the 2020 election that it becomes impossible. And worse, he will have equally unprecedented coattails, resulting in MAGA control of both Houses of Congress.
Their gambit is no Trump means no energy, low turnout, and the ability to plausibly rig the election. They could even concede to a RINO Presidential candidate while putting Dems in control of Congress. This helps them restore the equally divided country narrative and maintain control over elections.
What's sad is that many of their followers/cultists will believe it is indeed the end of democracy if Trump wins. However, there are a lot of people starting to ask, "What are they so afraid of? Things were actually better when Trump was in office the first time." Here's hoping that group doubles in size over the coming months.