Actually even a nutted wheel might have stayed together depending on the stiffness of the frame's rear triangle. Both ends of the axle are securely bolted to a dropout. A stiff rear triangle holds each end in place as a cantilever structure. They would have to separate by well over 1/4" for the balls to drop out, something a stiff frame wouldn't allow.

Back in the day we'd take in rear flat repairs on BMX bikes. We'd pull the wheel only to have the axles and balls spill out all over the floor. Customer ends up getting a new tube, new axle, and a hub service all for the $6.00 price of an installed tube (it was back in the bronze age).