Cost of advertising is a serious problem for generic drug makers. There are a lot of drugs where there exists an identical, cheaper, generic version, but the more expensive one gets sold because neither the doctors nor the patients have any idea that it exists. Hence all the "ask your doctor for x" ads, but the problem is that advertising on that scale, especially for low-incidence conditions, is very expensive compared to the amount of money you make, an so will result in just another expensive drug.
A celebrity putting their name on a drug company and then maybe mentioning it a few times publicly in places where normal people hear about it may make people who are facing very expensive drug bills look up the site and see if they make something useful for them.
If it’s the case where there’s an older generic and a newer product still under patent, that’s a discussion with your doctor: Is the newer product worth the money, or should I stick with the older thing?
In the longer term, success in the health space could add prestige to his name, ala the Nobel prize.
> The results show that the average annual price of top-selling cancer drugs in 2006, adjusted for inflation and secular changes in drug prices, have increased by US$154 and US$235 for branded and competitive brand drugs, respectively, following the 2010 ACA; however, generic oncology drug prices showed no significant changes.
Also he got to write his name on it