I’ve got to say, I am one of those DM’s who never thinks to include scrolls in treasure hordes. It was an act of conscious will that I remembered to include them in Castle of the Mad Archmage, but they’re really an incredible treasure item for a number of reasons.
First, of course, is their utility in deterring adventurers from using flaming oil. After the first time or two the party finds the charred remains of a scroll case in the debris from the giant spider webs they just torched with such abandon, perhaps they’ll be a bit more circumspect.
Second, they give the DM a controlled way to introduce higher-level spells into the game, as well as giving the players a chance to add spells to their spell books. A 3rd level magic-user can still be a formidable force when he has a scroll with lighting bolt, and it gives players a chance to add to their own spell books without having to find an enemy wizard to loot.
Don’t forget the scrolls!
Torched spider webs? Oh dear me no, that's what we brought a Dwarf with a 10' pole along for!
More seriously though, thinking about it, I probably was guilty of under-supplying scrolls (and even, to a lesser extent, potions). Really not quite sure why, they just somehow seemed to get overlooked.