But they could be. Elsewhere in this thread, I mentioned computer science is effectively a branch of physics now, because we can connect computation with thermodynamics, and e.g. put lower bounds on amount of energy required to perform certain computation. Therefore, if you consider experiences to be "execution", some specific computations done by our brains, then they still are physical things. Might be tricky to point and prod at them in the structure of our brain, but physical concepts that are smeared over space or time are nothing new - think e.g. waves, whether EM waves or mechanical waves or virtual waves, think of the boiling soup they make out of their medium, and how e.g. Fourier transform can tease them all apart anyway.