because the people working there are lazy fuckers just like all of us...
my friend izzy makes great pizza, I know of maybe one occasion he burned pizza and that was a summer day there was like 1 customer + me + him and the third guy angelo were standing by the window watching the chicks go by while I was enjoying my calzone, and we got caught up in the babe watching the pizza was overcooked....

moral of the story shit happens.