The claim doesn't logically hold together: it assumes a monopoly in medicine. It might not be profitable for the company with a treatment regimen to develop a cure. But for the company without the treatment regiment to develop a cure and take away all of a competitor's business and capture a significant part of it as their own? That's extremely profitable. You can charge far more for a cure than for a regular preventative treatment (per dose) so margins are far higher even if volume over time is lower. Suffice it to say cures are sufficiently profitable to enough of the actors in the system that they are worth exploring. And there is evidence of cures being researched successfully as referenced in the comment above. Also, I don't think all pharma companies are perfectly 'rational' actors in this sense. They are composed of people who got into medicine with the interest to help people, and those people know both cures and vaccines help more than just symptom mitigation. The motivation of the actors in the system to do good leads to even more research of cures and vaccines than the non-zero amount that is sufficiently incentivized (even if cures are less profitable than symptom mitigations).
