alt Hacker Newsit's not really like a 'live axle' from an older truck, it's more like a de-Dion style suspension (or dead axle).
https://en.wikipedia.org/wiki/De_Dion_suspension
you still see these in velocipede-style vehicles commonly.
and to your point : a dead axle is an effort to reduce unsprung weight compared to a live axle; it also lets you actually use alignment as a remediation for asymmetry issues rather than just pre-delivery straightening.
Ah, like on my old Volvo 340 ;-) They were fun, all that weight at the back (the diff and gearbox were bolted together under the rear floor) gave it excellent balance. Bit of a shame all that 50/50 weight distribution was only pushed along by a 1.4 Renault engine then, I guess.
Have you ever seen the Jaguar IRS setup? It's more like a twin-wishbone suspension *but the driveshaft is the upper link!* It's in compression and stops the hub tilting out, and the rear brakes are inboard to reduce weight even further.