Derrick Goold has the story.
Diapoules was somewhat interesting given some strong groundball rates but a rosy projection for him is a fringe bullpen arm. Houston Summers also had limited projection for long term success. Ultimately, the Cardinals have a crunch of A+/AA level pitchers and these two were squeezed out as a result.
Best of luck to Mark and Houston.
Also, in the same story, comes news that Francisco Samuel was being shut down with a lat strain. Could be a couple weeks, could be a lot longer.