Bikes have serious advantages over ATV's. They can get through hard scrabble and underbrush that would stop anything this side of a bulldozer. You can always dismount and walk, Vietcong style. And most of all they're a LOT quieter and don't scare off all the game in a ten mile radius. A surprising number of hunters use them.

For hauling, even 400 or 500 lbs is far from impossible. It mostly depends on how rough the terrain is.