Once you have removed the scramblers on all the towers, you unlock the Bushman, an improved variant of the P416. Stores also give more weapons for free per tower captured. It is because they cannot do business with remote villages, thus reward you for making it possible again. The natives once used these dilapidated towers as a means of communication between all of the towns, but when Hoyt landed on Rook, he ordered them to be taken over and used for his and Vaas's armies.