Seditious conspiracy comes with a max 20 years sentence (for one charge). Most people that day were caught up in the events as they unfolded without thinking through their actions and understanding what they were doing, to various degrees. They didn't wake up that day to start a coup but they did follow along with it, thus they were guilty but given leniency and their sentences were greatly reduced to reflect that. Those people got their 1-3 years for partaking.
Unlike those individuals this guy didn't just wake up knowing a coup would happen that day, he actually organized it. Through his direction actions and that of his co-conspirators the events of January 6th unfolded thanks to his efforts. Him and his co-conspirators who organized and created this coup are indirectly responsible for the violence that followed that day. So his sentencing wasn't lenient because of his leadership role coupled with the violence that occured he was given a stronger sentence.