You’re right that observing that we’re in a habitable universe doesn’t tell us anything. However, there are a lot more observations about the universe that we use in discussions about quantum mechanics. And some observations suit the idea that we’re know what’s going on better than others. “Know what’s going on” here means that a theory that is sufficient to explain all of reality in our local neighborhood is also followed more globally.
You’re right that observing that we’re in a habitable universe doesn’t tell us anything. However, there are a lot more observations about the universe that we use in discussions about quantum mechanics. And some observations suit the idea that we’re know what’s going on better than others. “Know what’s going on” here means that a theory that is sufficient to explain all of reality in our local neighborhood is also followed more globally.