So why do YOU think they did it?
Because Donald Trump told them that if he were not the President, they would lose their country. (This is, of course, just more Trump lies and hyperbole.) In his own words, on January 6: ""We fight like hell. And if you don't fight like hell, you're not going to have a country anymore." To suggest that means just "delay" doesn't make the least sense, since the end result -- according to his own hyperbole -- would be the loss of "their country."
You also said that after they "disrupted the process, they left." That's not quite true, either, is it? They left when Trump was finally persuaded to get on the air and say "we love you, but go home." Again, here are his own words, spoken on that day:
“I know your pain, I know you’re hurt, but you have to go home now, we have to have peace. We have to have law and order, we have to respect our great people in law and order [...] these are the things and events that happen when a sacred landslide election victory is so unceremoniously & viciously stripped away from great patriots who have been badly & unfairly treated for so long. Go home with love & in peace. Remember this day forever!”
They obeyed the only Commander-in-Chief they were going to follow, election be damned.