or it is all misinterpreted
the towers are archeo astronomy related structures that tell time
If we look at the facilities we have today, and try to imagine the past equivalents in a successful society, The frequency of the sites would indicate that either there was a severe need for protection (a very large and mobile raider population) or the sites served some utilitarian purpose.
The former could be verified or eliminated by excavating for the remnants of attacks, either military camp debris or evidence of walls being broached, burning, etc. Projectile points and such should be fairly abundant.
Storage for grain and/or silage (animal fodder), would make particular sense, considering the shorter transport distances from field to storage afforded by the number and distribution of sites. That, too should leave evidence in the forms of seeds or pollen or plant debris of a type likely to have been the results of agricultural or animal husbandry efforts, and may be supported by a lack of evidence of military action.
It would be possible for these sites to serve multiple uses as well, including both as grain/fodder storage, military defense, and be also aligned to foster astronomical measurements, although I would think the selection of site would be dominated by military considerations if that was the primary function, even distribution within an area if agriculture was paramount, and if in concert with other sites it served an astronomical purpose, the alignment and relative position of the sites would dominate site selection.