Because he's the president of the damn United States. It's his job to uphold the institutions that protect it, not to tear them down and throw them under the bus in the name of foreign interests... and himself..
So I assume you supported the war in Iraq right?
No, it's not Trump's job to blindly believe US Intelligence Agencies, especially when their record of getting things right post 2000 is hilariously bad. Honestly the entire thing should've been shut down after the Saddam WMD lie.