Note: I worked briefly as a contractor at JPL in 2011 on a project related to Curiosity image-processing and distribution (among other things).
I argued at the time (fairly strenuously) that the raw data (the data that was used by the scientists in this paper) should be public.
The reason the data is not released immediately to the public is both understandable and frustrating: scientists around the world compete for control of Curiosity's precious mission time. The mission is refreshed every day, each move is voted on and the results uploaded to the rover. The data is not released to give the "winning" scientists first crack at interpreting the data. It's about prestige - if you released the data and get "scooped" by Joe Public it's embarrassing but it's also a lost opportunity for scientific prestige.
The same basic reasoning is why so many JPL-produced datasets (particularly astronomical but also terrestrial - JPL does a lot of weather research) are not public.
Personally, I'd like to see this change. I want all publicly-funded non-military research projects have an open data policy. Clearly this would not apply to research with straight-up defense applications. But Mars rover data? I suspect that scientists will be incentivized without being granted artificial monopolies on that data.