I think there are two reasons.
1. It seems almost any fluid on the tires will improve traction somewhat. I think this may be because it is opening up the pores in the foam but I don't really know.
2. What I do know is that the actual rubber in the foam contains many solvents that evaporate over time causing the rubber to harden. Most compounds contain some of those solvents to help replenish the rubber and soften it.