Why we'll never see the 4 axle 315k cars as the next "standard"

No one want to acknowlege that all of the subs that I’ve worked on have a 143 ton “A” car weight restriction. 315,000# cars put you at 157.5 tons. Single car moves of in excess of 143 tons up to 157.5 tons are permitted if the car length is greater than or equal to 49’6". These cars must be seperated by at least 1 car weighing less than 143 tons to qualify as a single car move. No train consist may contain more than 10 of these cars. This would be a train blocking nightmare. There is alot more to this stuff than ya think.

440: you can’t just shorten the cars and run the 157.5 tons. Cars less than 49’6" are restricted to 143 tons and that weight decreases as the car gets shorter.

My point realy is to run short 143 ton cars instead of long 157 ton cars to have the same overall train weight and still use the lower axle load, or istead of using 3 axle trucks under long cars.

I know I read this in Trains Magazine at one time, but can someone explain why it would be a benefit for shippers to ship in 315,000 # cars? Thanks