We are coming to a point where many of us have every one of thier heros soulstoned. And more people joining this club each month. When this happen there is no value to the soulstones anymore. There isn't much value in climbing the tower of titans past lvl 25 if all your heros have a stone.
If we could do something with the stones like fuse them into a bunch of shards or trade them in for something good then people will continue to want to finish the tower.