You can beat cover three over the middle. The linebackers/safeties can't cover well enough so there will always be a window, even if it is small. Deep crossing routes, slants, in routes, etc.
Additionally, if there are no defensive pre-snap adjustments, curl and out routes will be open every time.
Finally, those deep thirds are one on ones with your WR. If you have a fast WR who can catch a contested ball, throw it up on a streak.
Deep ins should work against this coverage.