Well, that and the differences in the setting/magic (there's no Free Transfiguration in canon, for instance, and the Mirror is different - there are less Mysterious Ancient Artefacts generally - and Horcruxes run on different mechanics ... stuff like that.)

And Voldemort is just inherently smarter than everyone else, too, for no in-story reason I can discern; he just is, it's part of the conceit. (Although maybe that was Albus' fault too, somehow?)