I assume they want to wait for the re-exam to conclude since it may change the wording of the claims. Then with whatever the patent looks like after the re-exam they can sue for infringement. If they sued first, with the current wording, and the wording is changed by the USPTO, they would have to dismiss the first suit and sue again. It makes sense to wait and see how the re-exam turns out. It should happen sometime next year. Not that long in EDIG time scale.