" if you're an A380 operator with similarly little regard for the comfort levels of your cattle class passengers, then a reconfigured 380 will "comfortably" exceed the capacity of even the most densely packed 777..."
There's one factor discouraging that for an A380 operator: Freight capacity.
At full passenger load the A380 only has space for 7 freight pallets below decks thanks to their luggage (vs ~30 on a 777), but can carry twice the cargo mass of that same 777, for ~2000 more miles.
Freight is more valuable than people, so it makes sense to reduce passenger density upstairs to free up pallet space below. The resulting extra cabin space is a good sales tool and you can even package some of it up as "halo" class - bump some lucky stiff into it each flight for good PR and make money hand over fist when someone is rich and silly enough to actually pay for it.
Of course if you're an A380 operator that doesn't do much freight (BA, Air France) then using this aircraft is nonsensical and you need to run 75%+ loading to keep it profitable.