Noise abatement at a guess.
Many years ago, ATC/Pilots were jointly responsible for aircraft routings.
In the 80s and 90s, the aerodrome authority, (MA PLC), cultivated their 'good-neighbour' policy, and flexed their muscles, thus removing ATC's flexibility. Everything had to join final approach at least 7 miles out, in spite of the fact that a/c had become much, much quieter.
Still happens today. Much fuel wasted by imposing extra track-miles on aircraft types which make less noise than some road vehicles.
A shame.
Last edited by ZOOKER; 31st Jul 2012 at 23:01.