This. Graphite is a kind of solid lubricant, and you’ll frequently see it be used for all kinds of friction reduction purposes, both domestic and industrial. This also has the added benefit of any graphite based sliding contact being self-lubricating contact. Add to this the fact that graphite is a very decent electrical conductor with decent thermal and chemical stability, and you’ll see that the material underpinning pencil lead is very useful for electrical systems with a fast-moving sliding contacts. Plus, it’s fairly inexpensive. You’ll see graphite be used in all kinds of extremes, from lubricating door hinges to wire contacts for electric trains.
The same cannot be said for the waxy medium of coloured pencils. When it gets into tiny crevices, it’s more likely to gum up systems instead of making them run more easily.