When we were in the upper valley I counted 1 in 4 cars had a cracked windshield while waiting at a mall. If you have a tall truck you might get lucky, if you have a short car then maybe not so much. We had a car and had rock hits all the time. They were small and did no damage.
Seems to me that the quality of the roads are good, just not the cleanest. Also the cars and trucks that are using them could do much better as far as mud flaps and tires that fit inside the wheel wells.
I guess it's legal to drive with a crack windshield as long as it's not in your sight line in Texas. Reason why you see so many I think.