The best reason I can think of is that the buyer wanting a '74 7¼ is because he wants to change from a small bolt pattern rear axle to a big bolt pattern rear axle and NOT have to change the drive shaft. HOWEVER, the 7¼ has to come from a disk brake equipped '74 to have the BBP.
I just finished this swap on my 73 /6 car that I'm converting to disk brakes & BBP. Other than getting the danged u-bolts off, it was an easy swap. FWIW, Mopar put 7¼s on 273 HP cars with Torqueflite. I had one.