Why does graphite lose much of its lubricating ability without water vapour?

The lubricating ability of graphite is largely dependent on the presence of adsorbed films, specifically water vapour.1

While graphite is a layer-lattice solid with a crystal structure that allows its layers to slide over one another due to relatively weak van der Waals forces between them, this inherent structure is not the sole factor in its performance. In the absence of water vapour, these adsorbed films are not maintained, causing graphite to lose its lubricating properties and become abrasive.21