Perhaps EK is offloading at LGW as the nearest large airport to its origin, so it can turn round and get back to collect the next load of unlucky travellers.
Flying to MAN and back adds, what, 1 hour to each leg of the journey? They could be back over central Europe and on their way to lifting the next load by then.
Maybe it's just a way to shift quantity at the expense of quality.
At least they're trying.