WD40 leaves a deposit of slicone wax when it evaporates. In some circumstances this is an advantage, but in most mechanisms it causes a problem as the wax hardens with time, and attracts dust. This can lead to a vicious circle where you repeatedly spray more WD40 to free it again, and deposit a further layer of wax. Good for WD40 sales but not much else.

Good quick fix if you are not too worried about longer term, but that's about it.