I do not have proof to show, unfortunately. But I've been told by others that the removal of towering rewards was done because there was too many entering the game.

I firmly believe the best option would have been to remove 1k rewards and keep the 5k and 10k rewards. Those require a much larger amount of time to grasp and only keeping them around would not steamroll the towering community like the actual change did.
As much as I love to tower, not having an incentive for defending a tower makes the experience less fun. Even if people tower just out of the fun of it, much like I do, one still experiences a feeling of "what am I doing this for?"