I don't know if this is something to do with getting pax' weight distributed evenly or something else so I'm asking here.

I understand that an airline would want to block off Emergency row seats, but I'm curious about a pattern I'm seeing on an upcoming Boeing 777-200 flight which is consistent with all the others on this route.

Here it is:

....31 32 33 34
L--.X--0--0--0
K--.X--0--0--0
J--.X--0--X--X

G--.X--0--X--X
E--.X--0--0--0
D--.X--X--X--X

C--.X--0--X--X
B--.X--0--X--X
A--.X--0--X--X
....31 32 33 34

Seats marked X (row 31 GED) don't exist, the others form part of the Emergency Exit row.

We've booked ourselves into row 32 G&E (Bulkhead) but I was wondering why AZ routinely blocks 32D.

Can anyone explain this pattern?