Because there is no space on the sidelines, bringing the fans a lot closer to the wings.
SoL pitch isn’t as big as what we all think, the running track and the walkway around the bottom of the stand just make it seem roomier.
Based on last seasons Championship the SoL was 12th largest for playing area, Ipswich were 2nd largest (only behind Hull City).
When you actually look at the perimeter of our pitch, there’s a hell of a lot of wasted space, a slight change in the gradient on the lower bowl could get fans closer to the pitch (but obviously not under the cover of the roof) and squeeze in a few more fans.
I think that maybe the perimeter has (or had) to be a certain size to hold certain UEFA / FIFA games which is why so much space was wasted.