Good thought. I don't think its so long these days, but does seem ridiculous. Considering the amount of traffic Tan Son Nhut gets, the amount of taxiing seems crazy. My (wrong) theory is that after the war, as runways crumbled, they'd simply move to ones further out that are still OK. Another theory (probably wrong too) is that they make planes taxi alot so you "feel" you've arrived at a big airport. You can still see some of the blast-proof hangers generously coated in thick lichen as you trundle by.