Full lines but empty seats

I went to SFoT yesterday and noticed something new to me. On both New Texas Giant and Titan, the Flash Pass gatekeeper (the guy who holds people back in the regular line while letting Flash Pass users cut ahead) was not letting a sufficient number of guests on the ride to keep the ride full. As a result, the queues weren't full and both rides had between two and eight empty seats per deployment, many of them full rows.

I rode both rides at two different times and both times it was the same thing, the ride was underutilized due to the gatekeeper not letting enough people on the ride to keep the seats full.

Both of the gatekeeper guys were employees I had seen there before and weren't rookies. While I'm sure there is a reasonable explanation for this, I couldn't help but think of the possibility that this was a deliberate attempt to artificially increase the line length in order to promote Flash Pass sales.

Has anyone else seen this behavior at the parks? This is new to me.