According to google, around 10% of the world population is affected by diabetes. Far more are in a state of undiagnosed prediabetes that can be managed and prevented better if warned earlier, such a product would be very desirable. But at the very least, 10% of the world's population is a good number of people to branch out an investment.

Also, diabetes is one of those diseases that people manage, not cure. It won't stop existing or will end anytime soon, actually it's even expected to increase over the years. You'll always have clients for such a product and they tend to increase, hence the "infinite wealth" (which is an obvious exaggeration and meant as a hugely profitable), especially if you own a patent and are the only one selling it.