1. Trump is not getting back in, that is a hard fact. But something tells me that's not what the DNC is afraid of.
2. The DNC had no top-down plan to rig the 2020 Election but it's a lot more likely any fraud that could have occurred were a bunch of "stand alone complex" doings at the state and local levels.
@Secret Asshole has proposed a similar theory.
3. Going with the second point, this would mean there was fraud on a state or local level and the federal level Dems just rolled with it. If so much as a single shred of hard evidence gets found, that's a huge black mark and media blackouts can only go so far if it gets proven in court.
4. The Democrats are worried about the 2022 midterms. The House is likely a lost cause and the Senate is in a precarious position as it is. HR1 failed in the Senate. The coming second wave of lockdowns and COVID-19 restrictions might be a last-ditch attempt to fortify it all over again, but a lot less people are going to be as compliant.
5. If the 2022 midterms go badly enough, there's a possibility the GOP will have a large majority in both chambers of Congress. That means they can get a lot of shit done if they decide to actually do so (lol)
6. With points 4 and 5 taken into account, if it gets proven in a state court that so much as one instance of electoral fraud happened, even if it was a few sheboons or woke neckbeards on the local precinct level that were acting of their own accord with no support from up on high, that gives a GOP-controlled Congress an opening to impeach Biden and Kamala since the national level Dems just rolled with it.
Impeaching Trump twice, the second time being done after he was out of office no less, is enough of a precedent for politicized bullshit impeachments (tbh, the same can be said of the Republicans doing the same to Clinton in the 90's) and there's a good chance that if the audits prove something and it's in the public record, even the RINO types plus maybe Manchin will vote to impeach Biden and Kamala just to ensure their reelection.