Why so many blowouts?

There's also the possibility of over-inflation being the cause. So many people seem to think that the "correct" inflation pressure is the number molded into the text on the side of the tire, regardless of the actual load being carried, rather than getting their rig 4-corner weighed and inflating to the manufacturer's recommendation.

Over-inflation results in the tire having a curved profile at the road surface, with the center of the tread taking more of the load.

Also, the term "blow out" suggests an explosive failure, not a simple loss of pressure.