The hill giants have enslaved a large number of orcs to work in their kitchen, workrooms, and dungeons. (Dave Trampier from AD&D module G1: Steading of the Hill Giant Chief by Gary Gygax, TSR, 1978.)
The monsters in old modules aren’t always just sword fodder for PCs to fight. The orcs in the steading are ready to rise up against the hill giants if the PCs are willing to ally with them.