Even as there are eleven observed events so far, that is from 2 trillion galaxies in the observable universe [1]. So at 100 billion stars per galaxy [2] a guesstimate is that we are talking about 200 billion trillion stars. Seems even divided by eleven it seems pretty rare. (Not sure if the detector can “see” all those stars though.)
[1] https://en.m.wikipedia.org/wiki/Observable_universe
[2] https://www.livescience.com/56634-how-many-stars-are-in-the-...