The TSA program is called “Managed Inclusion”.
“But as wait times increased and security lines grew, the TSA implemented the Managed Inclusion Program starting in 2013, which allowed agents to pull low-risk passengers from regular lines and process them through PreCheck.”
TSA Ends Managed Inclusion Program


Managed Inclusion 11 ended September 13, 2015
(Yes there was a Managed Inclusion 1. I don’t know when that ended))


The new program, Managed Inclusion 111, will be rolled out shortly.
“…TSA will be rolling out a new program that will use canines to screen some travelers and allow then into the PreCheck lines.”
TSA Eliminated Free PreCheck to Make Room For... Free PreCheck! - View from the Wing



So now, agents + dogs will get you into the PreCheck line.


And now you know why your PreCheck line is snaking through the terminal.