Right now it costs about $750-$3000 to set up each monitoring site, so growers can only afford to install a low number of devices per acre [1], thus a high number of plants per device. In that case you’re not optimizing to anywhere the specific requirements of each plant, you’re assuming (often falsely) that all the plants in that area have the same needs as the one you’re monitoring.
The lower the cost per device, the higher your resolution and precision of monitoring can be, and the more you can accurately provide for the specific needs of each plant.
[1] Very often that number is zero.