Many, many houses of a certain size (but certainly not all!) have stages where sections can be readily removed to allow for a trap door. The challenge is that you then have to construct decking around the actual structure of your trap door to enclose it at stage level and to keep the top at stage level and be absolutely perfectly level with the stage for the show deck to them be built. That adds MANY further requirements to the physical needs of a venue - limiting where you can take the show even more, that takes a lot of truck space since the entire structure would really need to tour as a solid piece in most cases, that adds HOURS to the load in / load out time where you do not have hours to spare and need it to be a fast as possible... That is why if you see a trap door on a tour, it is going to be on the largest of tours that have a jump set that loads in early, a tour that has a lengthier break between each stop, or a shallow trap of some sort that is only several inches deep and fully contained in the show deck.