And our ability to detect exoplanets is both highly limited, and biased to large planets orbiting close to their sun.

Using our current technology to look at our solar system, we probably wouldn't see a habitable planet either.

Looking at https://science.nasa.gov/exoplanets/discoveries-dashboard/ , a planet with one earth mass and a 300 day year is simply outside of our ability to detect. Not to say that those are requirements for habitability; but they are requirements to detect the one habitable planet we know about.