I believe the official reason is to be respectful to the dead, but I suspect there is a lot practicality to it as well. The tombs aren't that big, there isn't r

I believe the official reason is to be respectful to the dead, but I suspect there is a lot practicality to it as well. The tombs aren't that big, there isn't really room for crowds to stand around a guide while they explain stuff. By not having guides, people go in-out quicker and it's easier to move around in there. If you do the free explore thing on OP's site, you might get a sense of the size. Imagine 10's of 30 people groups crowded inside those tombs, it would be a nightmare.