It was natural for explorers from Earth to go to the TRAPPIST-1 dwarf system as part of the first wave of interstellar exploration, once humans finally cracked the code on faster-than-light travel. The planetary system had seven confirmed exoplanets, and a remarkably tolerant habitable zone for a dwarf star; it was also extremely young by stellar standards. So it seemed unlikely that life would have developed so quickly there… thus making it probably safe enough for a species just starting to practice exploring the Galactic Arm.
This proved to be… incorrect. Not only were there three water worlds with functional biospheres: the other four planets all proved to have their own forms of life. And sentient races living on all of them, although admittedly none of those species were born there. It turns out that TRAPPIST-1 is well-named; it’s a favorite spot for monastic communities from all over this part of known space. Fortunately, humans were welcome enough… or at least their religious communities were.