1) TSA determines who gets PreCheck. Not the airlines.
2) The screeners at the airport have no basis on which to assess who is in the PreCheck line for what reason. Whether you are active military, signed up for PreCheck or Global Entry, or an airline elite, your boarding pass reads the same. For that reason, their "statistics" are pure speculation.
3) PreCheck's stated goal is to send as many people as possible through PreCheck. The goal is not to keep the line empty for a few people to sail through. As utilization increases, wait times will become more similar to today's wait times in the standard screening lanes. Enjoy the ride while it lasts.