Coupler to axle placement. Deck to axle centerline ratios are way different if built by anybody worth mentioning. The load placement for anything near rated capacity would make it dang near impossible to achieve without overloading the hitch point. Weight properly placed on a gooseneck is substantially higher at the coupler. This is the whole point to actually have the front axle carry a small percentage of weight, evenly planting the tow vehicle. I would argue a dually should be required to pull a gooseneck, even I own a single rear wheel. But my single rear wheel with capacity weight behind my gooseneck still out handles my 11 thousand pound tag camper all day.