None of those were profitable to treat, as they're infectious, contagious diseases which kill their victims and ultimately harm economies.

Dementia, on the other hand, is a disease of those who are past their productive lifetime as far as economic fitness goes (not being cruel here, just stating the fact from the perspective of those who view us as livestock), yet it does not kill the victim, and instead mandates care, therapy, drugs, and all the rest, over a period of years.

It is therefore highly profitable, causes a net generation of employment, and is not at all like polio, or typhoid, or smallpox.

>past their productive lifetime as far as economic fitness goes

One could argue that a cure for dementia would extend the productive lifetime of workers.

The vast majority of patients get it well past retirement age.

Polio kept survivors (the majority of those infected!) alive and in iron lungs for years.