GS/1K/Polaris use the 1K/Polaris line (can be quite a lot of people on a single flight)
*G/Plat/Gold/Silver use the Premier Access (if there) or regular line.
Most likely they're trying to push more people to use the kisoks (self-service) and the 'agents' there aren't UA agents, but contracted for baggage drop off / very simple questions / kisoks.