We simply have to focus on what we know until we find other examples of life. Think of it like a puzzle, you start with the edges and work in but also keep your eyes out. These instruments can detect a wide range of light, if there is something that doesn’t make sense right away we will surly investigate it more. We can and will do both, it’s just not the primary mission. A telescope to only look for something completely foreign and unknown is unlikely to get funding.