Robert Barron says
We are called to announce the good news to everyone, but not everyone will listen. Once we’ve done our work, we should move on and not obsess about those who won’t listen. Why do some respond and some don’t? Finally, that’s up to God.
Why do some respond and some don’t? Presumably it’s not due to God, but due to the people. This goes to the basic idea in Christianity that humans possess free will, and therefore are free to accept or reject a closer relationship with God.