I think some of the issue is that he doesn't feel like he deserves to be forgiven and in past games he has generally tried to set things up so that he's the person sacrificed, so his end game here may be to get Shiho elected and then get sold into debt slavery or whatever. Shiho is also known to be in Yuichi orbit and to fully trust him, so allowing her to become estranged from him means that she can get Shibe's support. If Shibe votes her then he can vote for her and make sure she has the most votes.
But I do find it pretty strange that people are acting like he still has exactly the same personality as when he was 8. Even if Shiho asked him for an explanation, she is definitely acting like she is tending towards believing the other people, people who are known to be far less reliable, or at least tending towards that in this moment. In truth, this has always been a hyper dramatic series, so maybe I shouldn't be surprised.