sbm12

This is part of it, but there are other reasons as well. Somewhat unique in the industry, JetBlue will assign seats for people in advance if they don't have them already. This will fill up the aisle/window seats that otherwise might remain available for customers who are actually thinking about it. I also believe that JetBlue will permit customers to select seats right up to the point that the aircraft is fully assigned (other than the ADA rows) rather than keeping some number of seats unassigned until check-in opens. This reduces the chance of getting one of those seats at OLCI.

In this case the large group was much more likely the cause.