Why not a 2 speed or quick change rear end option

Many years ago, such rear axles were available. They were quite common in Fords after WWII. They were Columbia 2-speed rear axles. They were GREAT!
Two and three speed "Brownies" (auxiliary transmissions) and rear axles were very common in trucks from ton and a half or two ton on up. Years ago, I drove a Ford F-4 (IIRC) that had an electric shift two speed rear axle with that horrible 4 speed straight tooth transmission. I was young then, and double clutching didn't bother me.