If the results are not to your liking, keep trying because the generation parameters change a lot with each attempt.
If a specific genre doesn't work for you, try a more general genre. For example: Try doom metal instead of uk doom metal.
Why are there sometimes more results than others?
Because we delete the ones that are repeated or that are too similar to the others. You can be confident with some certainty that the names generated are original, although it is likely that they are not.