In the training camp, only the trainees are in a fully closed training, unable to contact the outside world.
For the coaches, there aren't so many requirements.
Coaches can come and go freely.
Because coaches are well-known entertainers in the industry, apart from recording girl group selection shows, they have other commitments.
For example, someone like Chu Mufeng, a top celebrity, is almost working non-stop 365 days a year. Managing to spare some time to be the dance coach on "Idol Superstar" is due to his strong relationship with Ming Ge, plus it's an investment program of Star, so he definitely has to support it.
However, asking a top celebrity to go for over half a year or even longer without appearing in public would undoubtedly be a huge blow to his popularity, not worth the loss.
You can even take leave from filming to make a variety show or film an endorsement commercial!
