Because he's delusional and thinks anything to do with him adds value and/or elicits a positive emotional response: https://www.inputmag.com/culture/mark-zuckerberg-employees-c...

> Mark Zuckerberg is looking to develop virtual coins, nicknamed “Zuck bucks” by staff

That's not what the actual name will be.

Zuck bucks is quite obviously not what the virtual coin will be called when it's released.