Plus I suspect that there was a certain amount of inertia to design styles that caused a resistance to change.
You say tail wheels are bad for ground handling; maybe they are now they several generations have been trained on tricycle gear, but when that's all there was, perhaps the pilots just naturally handled them better. A bit like "Tailwheel? Looxury! We used to dream of havin 'tailwheel. We 'ad to get our ground crew to push down 'taxiway." "Groundcrew?..." etc etc.
I heard the development of the monoplane was called the 'Thick Wing' design and that once there was enough strength built into a single wing, it became the de-facto design as its thickness provided a place for gear to retract into, guns, fuel etc. Plus there was a benefitial aerodynamic factor as well. but that wasn't your question. Maybe it's because they can be (total wingspan greater) After all if you built a monoplane with the same wingspan as the total wingspan of a biplane, there's be a lot of torque a the wingtips and the wing would need extra structure to be self supporting. I think the size limits of living creatures follow a similar theory.