It all depends...
I doubt that either Zuckerberg or Elon Musk needs more exposure, because they are already very prominent business people. On the other hand you have Youtubers and Streamers that wants to stay relevant and they will fight in these exhibition fights to get maximum exposure for their social media presence.
I think these fights are orchestrated and planned and not worth my time and money to bet on. I watch the fights, but I will not pay to watch the fights.. if you understand what I am saying.
These celebrities and media's businessmen are constantly in need of new hypes and trends to maintain their exposure on the hot topics. You can see this by Elon Musk's actions, since he is constantly creating new polemics and giving unexpected statements to keep in evidence on news' portals.
Probably Zuckerberg is just trying to reproduce the same effect right now by challenging his opponent for a fight, as this kind of marketing has been working nicely for Musk for years already.
And even though you don't put any cents of dollar on their events, they still profit huge money just with your view. The more views they have, more money is collected from sponsors. So it's totally profitable for these celebrities to engage on such fights, at least until the public gets bored. Then they will have to create another hype... Maybe gladiator's games next time?

No matter how rich or famous you are, you always want more. Over time, they begin to see the world as a playground. They don't like it when they're prevented from doing what they want. I think that's exactly what Elon and Mark are in. They always want to be on the agenda and be remembered for different things.
That's why sometimes I don't want that much money to be accumulated in one person. While there are many things they can do, they try to get the attention of others. Sometimes I wonder if these people are alone. Is all they do just to increase their sociability?
I don't think they care if you invest money in events. They just aim to have fun by creating an agenda. They don't care what other people do.