And all cartels are obviously built around maximizing income, so I don't understand what 'illegitimate reasoning' would be. The same thing is still certainly happening today, but without the paper trail. A clear example of it is in the video game console industry. All the way up until the PS3 era of consoles, both Microsoft and Sony were heavily subsidizing their hardware. The video card in the original XBox was worth substantially more than the retail price of the system itself.
Then in the PS4 era they both stopped, at the same time and started releasing consoles in mid-range retail hardware with minimal subsidization. That makes 0 sense from a competitive point of view. If your main competition stops subsidizing their product, that's the exact time you subsidize harder than ever and claim the market for yourself. But it makes perfect sense if a couple of c-levels happened to have a chat and casually mentioned that ending the subsidization battles would end up being vastly more profitable for both of them. 'Yeah, I agree.'