Not being part of the design team, I can merely hazard a guess.
The low-drag high aspect ratio wing was part of the performance envelope optimisation, but gave substantial wing flexing from the no-lift full fuel state to the max all-up weight flight condition. This needed wing-tip auxiliary undercarriage wheels to keep the tips from dragging on the ground; these would have needed to be much stronger for wings that were intially 20ft closer to the ground. They would also of course have relieved wing-root bending to some extent; so optimisation is an interesting exercise.