Fast forward to today, and there is more openness. I did skim the paper mentioned here, but did not see any links to the actual data, which is a shame.
My understanding is that 70% of the difficulty medical research is collecting the data. So once you've done that you want to make sure you've protected your investment of time and energy.
From an individual stand point I understand why they do it. From a societal standpoint it's such a waste.
I'm guessing they don't, which makes findings, kinda, suspect.
Also their trove of data is not a one shot. They might collect data a mountain of data on Leukemia but publish one study on Leukemia's correlation with high power lines. Publishing this paper wouldn't necessitate opening up all of their data from either a horizontal or vertical perspective.
I see your point about using the data for other research. Hopefully reviewers of the paper, at least, get to look at the data.