Can you infer why P waves travel faster through the upper mantle
than they do through the crust?

Seismic waves travel more quickly through denser materials and therefore generally travel more quickly with depth. Based with that conclusion and with the average density of the crust being 2.2g/cm3 whilst the density of the upper mantle being 3.4g/cm3, and with the fact that the upper mantle is a solid, it would correlate that P waves would travel faster through the upper mantle.