I'm unsure what the question here is? Delta holds seats for gate release, so you could likely get an aisle/window if you tried on day of departure. Seat assignments are subject to change too, so if you had an aisle/window you could theoretically lose it. The reason Delta is doing poorly has to do with a lot of things, sales volume is not the sole indicator of profit. If you buy a Y/B/M fare, first class or are a Medallion member you could utilize preferred seating to secure a non middle seat.