[estpeter]

So how come they sit on the floor, don't build roads, can't build irrigation systems, grow crops, produce anything worthwhile?

[Non-Sequitur]

I'll narrow it down with a few assumptions if I may. First, I'll assume that you are talking about the area around what we now think of as Arabia, leaving out Iraq with had canals and irrigation from the Tigris and Euphratres Rivers for centuries prior to Islam. I'll also assume that you are talking about the 8th through 11th centuries when the men I posted about earlier lived because obviously today Arabia has all the things you mentioned.

OK, irrigation and crops. Irrigate from where? Grow crops where? In order to irrigate you need a large body of fresh water to draw from and, if you've ever looked at a map of the area, fresh water is sadly lacking. Now roads. Build roads for what? The camel was the animal best adapted for the area and it made a poor draft animal. Better to load it up and use the caravan trails. Produce anything worthwhile? Scientific knowledge may not be worthwhile in your opinion but the rest of the world, fortunately, thinks otherwise. Finally, sitting on the floor. I suppose that they could have built chairs, except that wood was in limited supply - that's one of the reasons it's called a 'desert'. So sitting on the floor beat standing around.

Hope this was helpful.