I'd say at least 90% will be passionate about music or performing with the other 10% being super talented/ geniuses.
Without being passionate they won't make it in the industry. There is intense amount of competition these days. They have to train basically 24/7 from 12yo just for a slim chance to debut. I hear those trainee audition programs generally can have up to 10,000 applicants for like 10 spots and then maybe only a few of them end up being able to debut in a group.
Even Huh Yunjin was about to quit and enrolled in college in the USA. But she received a call at the last minute to debut in LSF and shes super passionate.
Of course a lot will also be doing it for the fame and celebrity status as well but they will still be passionate about performing and singing as that is what they will be doing 24/7 as a trainee.