That's the reason (at least in the store I used to work).
Also, in some stores, the clients drop the items they don't want, and the employees have to fold them back (or put them on a hanger) and to put them back at their correct place in the store. It builds quickly, and you want to keept it manageable.
I've seen people in primark pick stuff off a rail, hold it up to themselves to size it, then if not happy just drop it on the floor and reach for another. It amazes me and not in a good way.
I probably has more to do with not wanting too many items to be simultaneously unavailable for other customers, which makes sense.
At least that's how I always viewed it, maybe someone can confirm or deny.