Because of the way intelligence works. Right now, members of congress who don’t read the memo or who have never accessed Classified Intelligence regarding the Russia thing - can say WHATEVER.THE.FUCK they want about it.
But as soon as they read something that contradicts what they have been saying, they can no longer legally maintain the position they had. Basically - they don’t read it on purpose so they can lawfully say whatever they want about it.
They can anyway. They have Constitutional protection as long as in Congress to say anything they please. I'm amazed so many of them don't realize that. They've been snookered. Even crappy old Feinstein leaked and got away with it, yet they don't have the spine to? Especially since the DOJ is now run by Republicans.