That's because far too often the dancers did things down there that were not so beautiful. In fact, far too often, it could get pretty raunchy. Just remember, for them, this isn't an exotic mysterious dance. This is what everybody grows up doing. So when they dance, they don't have a conciousness of perpetuating an art form. They're making a living and expressing their personality through the dance. Some personalities are not too wholesome....Really! Wow I did not know that. That is so sad to see shackles of sort put on a beautiful dance form.
There are travelers accounts from the 19th century that describe dancers decending to the floor and doing a kneeling backbend. In the realm of social dance, you can still see this done, as well as dancing in a kneeling position, or with crossed legs. Lucy would always go down to the floor and do some arm and hand flurishes with crossed legs. Somewhere I have a picture of the two of us doing that. I use to have another photo with the dancer of the Hassan Hassan troupe where we did some moves on the knees before she went into a backbend. Whatever the case, It's kind of old school today, like playing cymbals, but as social dance you still see it. Sometimes they lay on their side and do a leg shimmy, but this is considered very low class. Here's a video of some guys in Egypt, one does some floor work. https://www.youtube.com/watch?v=XMJAdhMNQf4