A library is never fully silent, pages turning, a distant cough, soft footsteps are always somewhere in the background. But those sounds carry a message, everyone here is focused, and that message reassures the mind.
Silence at home doesn't carry the same sounds, so the mind has no reference point. The calming feeling of a library doesn't actually come from silence, it comes from a shared atmosphere of focus.
You can't fully recreate that atmosphere at home, but a light sound texture with a bit of human warmth to it can create a similar sense of reassurance.