The intel agencies don't have a perfect track record, they don't mind thousands of deaths, they crave boogiemen, and everybody on earth knows Trump believes the establishment appointees of the last 3 administrations are attacking him without evidence. And there is no evidence. Trump's not a guy to stand on decorum. He picks his lies, and this is a time he's not going to tell a lie. He doesn't trust the establishment intel formed by John Brennan. If he lied and said he trusted the agencies established by his political opponents, everyone would know he's lying. We all know our government isn't a monolith. So why fake it? It would also be a strategic blunder, because it would cast doubt on the legitimacy of his election win. He would make a lot of people happy, but it would be an idiot move.
I guess if you're convinced without evidence that Putin has blackmail ammo on Trump, then maybe Putin has some kind of hand. But Trump understands leverage as well as most people, and we are giants compared to Russia. Trump said on the RNC debate stage that he'd be willing to meet with Putin, and he's going around offering every worthwhile country a fresh deal, individually. he doesn't like dealing with unions.
He does things differently. He said he would. That's why a bunch of people voted for him. It's not treason.