Simple answer:

1) In order for initial results to be released before the respective publication, they need to have a "public outreach value", like images, or data from "life experiments". In this case, parts of this data is released in a form of a few plots or discussed in interviews, and if it is images, well you get the real thing. But what actually is the public outreach value of radar data? Obviously, it is non-existent! How exciting could some altitude data actually be for the public? The only way that they would be exciting would have been if they show that the topography data that radar recorded indicated waves or maybe a crater or something significant. But almost no topography is seen in radar data

2) There are laws regulating the release of the data. The radar data is used for a project called "Descent Trajectory Reconstruction" and among the rules of the group working on this is that no data is released until the first relevant publication occurs. This is common for most instruments. Now, you might say: is releasing just a plot in jpg format will cause them problems with these regulations? Is somebody going to steal data from looking at these plots? Of course not. If you want an answer for this, refer to 1