Elisabeth Rosenthal wrote An American Sickness about this phenomenon. This essay is a good preview: How Economic Incentives have Created our Dysfunctional US Medical Market - https://medium.com/@RosenthalHealth/how-economic-incentives-...
It might be true if there was only one pharma company, but surely most companies would prefer that you buy their one-time cure than become a lifetime customer of their competitors. Diabetes is a particularly bad example because an ungodly amount of time and money has been spent trying to protect, repair, or regrow beta cells. Despite this, we have made very little progress. However, Accu-Chek is not bribing researchers to tank their experiments in the hopes of selling more test strips. The problem is that biology is absurdly complex and messy.
Plus, we have a nice counter-example. Until recently, patients with Hepatitis C were treated with a long course of interferon (6 months to a year), with relatively mixed results and fairly nasty side effects. About 50% of patients did not clear the virus, and needed liver transplants.
In 2013-4, Gilead got approval for sofosbuvir, which needs to be taken for only 12 weeks, has a much higher cure rate, and more mild side effects. To be fair, it is eye-wateringly expensive, especially in the US, but that's one way to make 'cures' work.
Before the middle of the 20th century, linseed oil and soybean oil were drying oils that were used to make stain and paint. When the paint producers figured out how to make paint from petroleum, the seed oil industry rebranded their product as "vegetable oil".
It's much harder to fund "we have to completely rework our public health infrastructure" (in the US, at least), then "We can help save these lives in <insert relatively short timeframe>".