They've only been claiming election fraud for decades, and spent millions (maybe billions, by now) in taxpayer dollars trying to find any kind of significant fraud that wasn't from Republicans. They've never once found the smoking gun they promised, which includes Trump's failed special commission while he was in office.
But they're never going to stop pushing that narrative, because they are literally trying to destroy democracy. They want a dictatorship where elections are meaningless and they retain power no matter what. It's been their goal for a long time, and they've stopped pretending otherwise.
As the article points out, they're determined to bull through anyway. But the effort is doomed to failure. Even if they achieve victory conditions (effectively ending democracy) it won't last. It'll just make the next revolution that much more painful. But their sense of entitlement won't allow them to stop.