Are you against all lossy compression methods as well? The watermark can simply be a slight tweak of the compression algorithm that could as well have been done for non-watermarking reasons.
The whole point of lossy compression is that it tries to be inaudible, as a primary concern.
The whole point of audio watermarking is that it survives lossy compression. Inaudibility is merely a secondary concern.
This is an adversarial relationship, and one that the audio watermarking is doomed to lose. By and large, lossy codecs succeed in transparency, and therefore as an inevitable consequence, watermarking fails at it. After decades of development, lossy codecs are just too good - there's nowhere left to hide information.
(It's also worth noting that the consumer benefits from the quality tradeoff that compression makes, in the form of decreased storage and bandwidth. They don't benefit from the audio watermarking at all.)
There are always going to be some subjective decisions in the lossy encoding process. Determining which bits to drop via encoder configurations/customization is far from an exact science. These decisions themselves can act as a watermark.
At sufficiently high bitrates modern lossy codecs are transparent. Even MP3, a dinosaur of a lossy codec is transparent (as in nobody can successfully ABX it) for a lot of music starting somewhere in the neighborhood of 192kbps, and at the 320kbps that commercial stores sell MP3s it is transparent for all physically generated music so far tested (some electronic music with incredibly fast attacks can have audible artifacts).
No, as was already explained upthread, "the watermark is supposed to survive being re-encoded, so it can’t be something just in the compression algorithm". It needs to be something that survives no matter which subjective decisions the lossy encoder makes.