I suspect that a lot of ill people, and people with loved ones who are ill, spend an enormous amount of time reading every paper they can find on the illness, or trying to narrow symptoms down to a particular illness. That's also a situation where you can go through 50 papers easily for every useful one (or even intelligible one, if you're a layman) you find, so a definite sci-hub situation unless you're independently wealthy. It's the requests that draw (or once drew, right now I guess) stuff into the database.