If he is already rich enough, he may not need bitcoin, although I find your argument too simplistic and I would like to know your friend's level of 'rich'. Do you know approximately how much wealth he has?
Anyway, it is a bad idea to try to change people's minds on financial matters.
I disagree with your line of thinking. I think rich people may need Bitcoin the most, as it is an incredible store of value and when shit hits the fan rich people could end up with nothing like everyone else. Bitcoin is most valuable as an insurance policy, so it is arguably more important for rich people who want to maintain their living conditions than for “poor” people who may have more immediate concerns than investing for future wealth.