During the last few years the performance of our computers has increased while their size has been reduced. But there is a physical limit on this development because quantum effects play a significant role on very small sized transistors.
In general the rule in optics is that a large image sided NA means a small minimum spot size. So steeply focused, diffraction limited beams result in a very fine spot. Thus scan lenses with short focal lengths and large input beam diameters can achieve a smaller focus diameter than lenses with long focal lengths and small input beams.