Originally Posted by
champair79
I work for the airline and actually asked the same question when I was lucky enough to have 2 seats to myself and wanted to put the armrests up to make a sort of bed.
The reply I got was that the backs of the seats are wider to improve passenger comfort. This has had the effect of reducing the gap between the seats to less than the armrest width so the decision was taken to prioritise having a slightly wider seat over the armrest going fully up.
The railways in Britain overcame this one about a century ago (you don't see it so much now, but that's progress) by having the armrest just lift into a depression of it's own shape between the two seats. All the remainder of the seat backs is full width.
Send the seat designers down to a railway museum to see how to do it.