The study write-ups are often press releases from universities’ PR departments. Others are from organizations that sponsored the work or hospitals the researchers or doctors were from.
Medical Xpress just seems to get the most, out of the available sites. They do have some people do write-ups from studies that otherwise didn't have a release to utilize, though.
I am wading through the garbage, not unlike how PJ-Comix wades through Democrat Underground and other crazy liberal sites.
I couldn't handle frequenting those sites, but I can somehow handle Medical Xpress.