Not the author, and it's a totally reasonable suggestion, but having done it, one decent reason is that baking the Ptex into textures that actually fit in the 2

Not the author, and it's a totally reasonable suggestion, but having done it, one decent reason is that baking the Ptex into textures that actually fit in the 2070's ram requires making camera specific resolution decisions, adding gutters between adjacent textures, and probably still using out of core texture loading anyway. In other words, it's doable but not easy. In the Moana dataset, the textures consume quite a bit more space than the geometry IIRC.