There definitely are ways that publishers could have avoided falling foul of anti-Cartel legislation (my question was about where the line is, ie if they did it legally would it actually benefit them), but...

Spotify and Netflix aren't owned or created by a syndicate of all the major publishers, so that's not actually a counter point. There's a huge difference legally speaking between a company negotiating with lots of rights holders to offer customers all of their content in one place, vs. those rights holders co-creating that platform and running it themselves.

(Not that the distributor has to be owned by a cartel of the rights holders to still abuse their position illegally, eg https://www.justice.gov/archives/opa/blog/e-book-retailers-d... - it's just that the cartel aspect is the bit I had been talking about.)