Well I always assumed because they were not experenced enough (or smart enough), but mostly not experenced,oh and probly there for canon fodder purposes. Pretty much all the ace flyers I'v seen in the series change there modes multiple times in a dog fights, heck look at the battle between Isamu and Guild in M+, or Max and Millia in SDFM.
I always thought of this manuver as a "I'll luanch all I have, and hope I hit them and wittle there numbers down" thing. That and it looks pimp when an Itano circus is let loose.