The Room of Requirement has a particular chamber for people to hide stuff. Everyone needing a hiding spot is redirected to the same chamber. It goes without saying that several hundreds of people have used the same chamber for hiding stuff.
It makes sense - what better place to hide your secrets than under a pile of other people's things?
... Well, it makes sense today, because there's so much junk. But what about the first users? Let me put it this way:
Suppose that the first ever user is a boy A:
A needs to hide something, and discovers the Room of Requirement. There, he finds a nice, empty space where he can hide his... oh I don't know, dead body or something. A places the dead body there and leaves the room happily, knowing that this magical chamber will do as he wished: keep the body hidden.
Then B, another boy, needs to hide something. He finds the Room of Requirement, and is granted access to a nice chamber... with a dead body in the middle.
The point of a hiding spot is for your possessions to not be found by anyone. This doesn't make sense for the first hundred of users of the Room of Requirement, because one user will find the possessions of the previous users.
It takes several hundred users to make this a good hiding spot, but for the first ones this must have been a bad one, because the objects are right there in plain sight, rather than a large pile of garbage.
My question is, then: why did the Room of Requirement use the same hiding chamber for all the people that needed to hide things? If A asks for a place to hide his corpse, obviously he wishes nobody to find it. Yet B will find it.