If you used "suljettu" in this case it would most likely mean that the theatre is closed for good, i.e. it won't be opening again, at least not anytime soon. Maybe the threatre went bankrupt, or it's under renovation for a year etc. Using "kiinni" more easily lets you understand that the theatre is just closed for the day and will open tomorrow, the day after etc. So, while both are in use, there's a slight difference in meaning/usage.