Because they only want to accept an external locus of control, where everything but their own actions gave them the bad health.
I wonder how many gay men lost their lives to AIDS because we were too afraid to point out the dangers of their lifestyle. And AIDS is more about having sex with many many partners than anal sex. After all AIDS is a virus and like all viruses the more people exposed and contract it the more people spread it, the more people catch it, the more people spread it, etc. etc. and then you have an epidemic. But we can't (or couldn't) point out the obvious because that would be homophobic. Worst of all AIDS is preventable and the cause is blazingly clear. There is absolutely no doubt how a person gets it unlike most cancers and even heart disease.