My OCD kicked in, so I just went over to check out Ticketmaster again. The lower tier is virtually sold out. I did a rough count and it looks to be a little less than 300 tickets available and they're all located in the Batters Eye, Audi and Delta sections (with the "Resale" function turned off).
Unless they're holding back sections (as mentioned before) I can't for the life of me understand why the 300's at least aren't being made available.
NYCFC Watch tweeted that they are opening the 300 level. Haven't seen it happen on TM yet, however.
EDIT: 4 sections now up for sale in 300 level on Ticketmaster.