While I generally agree the majority of the stuff on a tablet justifies the whole screen at all time, things people can do may not be limited to just a single app, particularly in the area of productivity. For example, one might want to cross-reference PDFs alongside typing your document. I can't see why splitting screen would be worse than swipe, swipe and swipe in these, perhaps niche, cases.
But of course there are better solutions in the above case, like a properly implemented multi-tab office suite with an in-built document viewer, instead of seas of individual apps... Moreover, I guess the need may not be as high as in the last decade after all, as people own lots of devices that one may eventually multitasking by making use of the devices, ugh.