The attack wasn't because of any legitimate wrong that the US government did, even though there are many, MANY examples they could have chosen. They invaded Capitol Hill with the explicit purpose of overthrowing the government and undoing the 2020 election because Trump said that the election was rigged with absolutely no evidence. In case you remember, he almost did the same thing in 2016, and said that he would only accept the election results if he won. Trump can't handle losing, many Trump supporters have cult-like devotion to him, and him continuing to denounce the election results led to this terrorist attack.