Cell towers are generally located near each other because when AT&T comes to town, they have to spend a lot of time and money on radio frequency analysis to determine the best locations of their antennae for the network to function properly with respect to terrain, elevation, buildings and trees in the way, willing landlords, zoning regulations, and public resistance to an ugly cell tower in their backyard.
Then, when Sprint-Nextel comes to town, they already know where the good spot is and do not have to spend the money on reinventing the wheel to design where their antennae will be placed for their network.
Also, cities have zoning regulations in place severely limiting where new towers can go. So often times they end up next to each other, generally in commercial, multifamily, and industrial zoned lands if not actually on the same pole, i.e. carriers T-Mobile and Sprint are pretty much forced by the hand of local government to physically locate on AT&T's tower to reduce the proliferation of new towers sprouting up like weeds across the landscape.
Whether or not these towers can selectively pick out a house and microwave everyone in it... I'm not sure. But I bet, if your phone was powered off the cops and cell towers would have no idea where you are at, thus no target.