Trump and Warren aren't the only two candidates. Just because Warren might be worse for their business than Trump doesn't preclude someone else being better for it than both of them.

And personally, I'd prefer if they banned election campaign ads, and other election-related advertising, from all sides (including people who aren't part of either party), instead of subjectively approving only ads they consider sufficiently honest. They, and any other corporation (be it a sole proprietorship or a trillion-dollar monopoly behemoth), shouldn't be in the business of "curating the truth" for the public.