There's certainly a measure of hindsight involved. But we shouldn't confuse being shocked with not being surprised. He had spent years creating a loyal following. There's a reason they came to be seen as a religious cult.
In the summer, Trump's former Secretary of Defense (Mattis) and former Chief of Staff (Kelly) warned America that
Trump was a threat to the Constitution. Almost
500 Generals, Admirals, and security officers signed an endorsement for Biden. Trump was spending his time creating distrust and hate towards the American elections. And as he began to lose, Trump immediately fueled his cult into action to reject and protest. As November and December played out, Trump's viciousness and wild accusations became more and more desperate. He tried to stop everything, from the actual count on November 3rd, to the Electoral blessing on January 6th. The man even tried to order state Republican to find votes before pressuring his own VP to simply hand him a victory.
So, on the very last day of this journey, January 6th, when Trump and his coven of traitors raged in D.C. and excited the cult to march down to the Capitol Building and show strength, that's exactly what they did. It shocked us what they were allowed to do. But it was not surprising. For anybody who did not listen to his tantrum of a speech, all they had to do was take a look afterwards and say "well, no wonder."