One of the main reasons why the A380 Pax is a bad freighter is floor load. Reinforcing it, the floor of a Pax A380, is not economically abd Airbus never built a dedicated freighter version of. Which is a pitty, because more often than not cargo capacity is limited by volume and not weight.

If at any rate possible, it is avoided to open the nose of a 747, tue cabin is pressurized and sealing it again properly is major PITA. That, and most 747 freighters started their lives as Pax planes, and tjose noses cannot be be opened anyway.

Through loading is obly helpful for long cargo, andbyou can even squeeze 10 foot containers through the cargo door of a MD-11. Which leaves the odd specialty cargo job and military applications. And for RoRo loading, the 747 nose is too far above the ground.

Yeah the 747 was originally designed as a freighter in the first place, the A380 wasn't