How would The Avengers know Chuck had anything to do with it? They'd blame Bolivar Trask and go after him or be mad enough to destroy all of the Sentinels in existence. And that would inadvertently play into Xavier's machinations too.
The only way they could pin it on Xavier is if they had their own telepath and The Avengers have always been too stupid to realize they really need to have a team telepath considering how many telepathic mutants are roaming the streets. They booted Moondragon out and haven't replaced that power set since.
With all the mystics they have at their disposal they could find out if he's been tampered with. Just like they would have found that Spock wasnt right if he didn't run.