I doubt a 4x4 single isle aircraft would be able to be certified by the FAA. No way to safety evacuate passengers in enough time unless you put exits all over the thing (not practical to design and the fact you would be limiting who could sit in those rows because of exit row requirements)

Not enough overhead space if it was single isle too. At least a double isle can fit more bags above. I don't see pax demanding that type of seating.