Originally Posted by
WheelsFirst
American reserves a large number of seats for elites and full fare pax, these aren't MCE or preferred, just regular seats around the middle of the plane. These seats open up at T-24, and are probably the ones you saw.
All kinds of speculation in this thread, but the correct answer is in the quote above. The non-middle seats are not necessarily assigned, they are merely reserved for elites. That is why they become available at the last minute.
I cannot speak to motive, but it may be purely to save some non-middle seats for elites. In other words, sometimes a cigar is just a cigar.