I am not any expert in this area, but I believe the short answer is... because all purpose flour is the most easily found in grocery stores, and secondly, most people ( 99% of these so-called expert sites that give out pizza dough recipes really don't have a clue what they are talking about. )
Yes that's a pretty general statement, but I believe it to be very true. Many of the very top websites for recipes are ones really for doughs that most people make, and most of them call for all purpose flour. I just don't think these sites are educated on the fact that real pizza places use very high gluten flour.
You won't find any pizza sites out there owned by owers of real pizza places willing to give out there secret recipe for dough, - most of us at one time or other have scoured the net for "real" pizza recipes from reall pizza places and they are just not found.
One guy that used to frequent our club site here, worked at a pizza place... he gave out a recipe, and a day or 2 later he lost his job. Not good stuff. Some son of a gun must have turned him in, either they overheard him talking about his posting of the secret recipe, and wanted to get him in trouble.
Anyway many others can jump in on this topic.
Btw, thanks to the owner of the site, Steve updated software, and your quick response was because we have a new option available to us now that lets us get email notifications of ALL new posts to our
The Pizza Lover.