Every billionaire has incentive to make public statements influencing their competitors while not doing what they say. If everyone else reduces production, you get to take the excess.
See the repeated prisoner's dilemma, where the fact that you keep repeating the game completely changes what it means to have an optimal strategy. A company doesn't make a choice to collude or not once, they make it over and over again.
Billionaires and corporations collude every day via Signal, Telegram, WhatsApp, etc. We've just made it almost impossible for them to leave a paper trail, and for us to prove it. Thus we get lots of people defending their actions as "just business" or something: plausible deniability is all most people need.
It made less sense back when billionaires needed to get on trains and spend hours to collude. Now they just make podcast appearances.
See the prisoner's dilemma.