Yes, you are missing that this is typically a result of not being able to give up seating, a need for the security offered by an enclosed space or simply no one there to speak out against it. It really is simple, you can't mix for the audience if you don't know what they are hearing. It has been years since I worked on a theater that could only mix from the booth and that didn't have an alternate mix position or at least a tech rehearsal position out in the house. Oh, an here is an online picture of a private school theatre with a mix and lighting position out in the house, The Murray Arts Center : Mount Paran Christian School (and yes, that is an SSL C200 digital console at FOH, one of four SSL consoles in a building with very comprehensive technical facilities). Here's a larger space that serves as a community arts center as well as serving the adjacent public high school that has a mix position out in the house, NPAC - Home. Both spaces also have enclosed booths at the rear of the house that can be used for events that don't require significant mixing.Am I missing somethings? All the pics I see online have them inside :/
As far as an pre-manufactured enclosure meeting all codes, no, that is not necessarily true. It may meet national codes as far as its construction but it may not meet all local codes and how it is implemented and integrated into the space must still be addressed. If it is enclosed there may be not only electrical connections but also mechanical system connections, voice/data connections, life safety connections, etc. Also think of how you are going to get all the related technology (lighting, comms, audio, etc.) to and into the booth.