Its a pain in the ass to lug around a lot of liftables or many inventories full of items up and down taller buildings like great halls, stone towers, and windmills, lets add dumbwaiters. Mine elevators already exist and are almost identical in function, so why not just add a special one which can be put into buildings for similar use
Bonus points if they could be potentially built into the wall itself to avoid wasting floor-space on them.