Because science depends on the external world, and there might always be hidden variables that we are not considering, it can only give us extremely high confidence after we make repeated observations using different methods, but it cannot give us the absolute confidence that Math can give us.
Also, this example of faulty telescopes is actually really close to what actually happened in the history of astronomy. Stars were thought to have a visible radius that made them appear to be much larger than the Sun, which was considered evidence that the Sun was not a regular star.