It's just the classicising influence on art generally - the statue of Washington as Zeus was rejected almost instantly by everybody and stashed in a basement - not because it deified Washington but because it showed him essentially naked. The "Apotheosis of Washington" is a little bit over the top, but pretty much according to form - you can find all sorts of famous persons "apotheosized" in similar situations.
My personal favorite is the horrendous sentimental mish-mash of goofy (fake) Celtic mythology and French romantic tackiness in Girodet's "Apothéose des héros français morts pour la patrie pendant la guerre de la liberté" of 1805:
This is so outstandingly BAD that you don't really know where to start. The whole thing is based on McPherson's fraudulent "Ossian" poems, which took Europe by storm to the point that everybody was stuck pretending they were real. The blind bard Ossian is welcoming Napoleon's dead generals, Joubert and Hoche among them, into paradise. The Gallic rooster and Victory are chasing off the Austrian eagle . . . all sorts of other silly stuff going on.