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.
Then why are they even bothering trying to arrest him and such? If they knew they can just steal it again they'd happily let him run unimpeded and "lose" just so they can point and laugh and make their claims that MAGA is washed up and fading.