I will be flying soon on the same flight as someone I know, but we booked separately. I was hoping that we could adjust our seat selections so that we could sit next to each other, but for some reason when I select desirable rows, the available seat(s) next to me suddenly become "unavailable" (X'd out). You can see an example of two locations in the airplane where this happened below. I've never experienced this before. Why do they seem to want to hold the seat next to me, no matter where I sit?
(Note, if you are unfamiliar with Delta seat maps, the green seat is me -- I have redacted my initials for privacy)