I think people started to realize it this year or so. Since Sony more or less did nothing to improve the output of the jack for like 4 generations now. I think two things happened that stopped people from realizing that.

1. they brought back the jack the same year LG left more or less. This lead to a bunch of LG users wanting to go to Sony because they had similar hardware like the jack and expandable storage.

2. people thought they would integrate their walkman lineup like they did with their camera lineup/tv lineup.