Marketing- it gets people to believe the equipment is balanced and in the case of many, it's not.
If the source equipment isn't far from the preamp and the preamp isn't far from the power amp(s), balanced LoZ isn't even needed- the reason it was used in the beginning is that it's the best way to connect, but also because nobody had come along with RCA plugs and jacks. In reality, if the equipment chassis were in contact, a negative connection on a shield wasn't needed until someone got the idea to isolate the audio negative/common from the chassis.
It's possible to have hum when using balanced cables- I installed an AV system where the electrician didn't run the feed for the outlets on one end of the cabinet from the box on the other end. I didn't want or have the space for a wad of extra cable in the cabinet, so I made the cables using Canare and Neutrik ends- there was no resistance on any of the wires, but it hummed and it didn't matter which cable was connected, so I tried an unbalanced cable and it was silent, so I made a set, took the balanced cables with me and didn't charge for them.
Parasound isn't complimentary balanced circuitry either, at least at the time when I asked their tech support people about it.