Well, it's now at W7 Y7. Looks like there's 8 C+ seats open, so they probably also opened the additional Y seats knowing that most of those C+ seats will be filled with upgrades (or they can put BE pax in them if not filled by upgrades). The flight on the 24th is down to Y4 and is also showing quite a few seats open in Main. My guess is it's just a fair number of BE pax on these flights who haven't been given seats yet and they'll start getting filled up as seats start to get assigned at 24 hour mark.

BE/Main fare differentials are $45 one-way on this route, so it's not too surprising that there might be a good number of people in BE given that this route is likely heavy on leisure flyers.