It's not their risk to take. Getting a drug to market is a complex process that can be derailed by any number of mistakes ranging from the mundane like improper blood draw during clinical trials to the tragic like accidental deaths that puts public pressure on the FDA to shut it down or spook away investors. Any hiccup in this process can kill it and once a patent expires, the chances of someone bringing that drug to market is almost zero, regardless of its efficacy.

The vast majority of drugs and therapies are developed via private investment and many companies go public before they make even a cent of revenue to fund the clinical trials. Public sentiment is the driving force behind their stock prices because they're literally forbidden from making money until the FDA approves their drug. Lots of them go bankrupt every year before finishing clinical trials or releasing a product and rushing the process is quick ticket there.

Patients don't get to put at risk the decades of good a drug can do because they're desperate and afraid of dying.