Because people want to find lives,resource and some planet which is suit for people live.
Why Do People Explore Space?
We can find if theres life beyond earth and us, humans are curious about finding new planets, stars, and moons.
They want to explore new moons, planets, stars, etc... And see if people can live in different planets.
To find life in extraterrestiral habitats and prepare for perminate human presence on other planets