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.
In these times, there are still many rich people who have no interest in Bitcoin. The only ones who are always interested in it are the rich, who see this great potential and want to increase their wealth, so they buy it.
Yes, it is true that it is still too early for others that Bitcoin can be considered very young compared to other opportunities that have been in the industry for decades like this, but change Bitcoin, because many people have become aware and others have made a living even hope because of Bitcoin because they had a new solution to their financial problems.