Lgw is suffering from the herd mentality amongst airlines. One moves to Lhr for a few flights, they all have to move. If the slot rules are not relaxed by the winter season, many if not all of them will have to return to Lgw. So what was the point for a few flights? Lgw is also suffering from a cautious approach from Ezy to restarting flights. They may need to show a bit more commitment.
And remember, these higher yields from Lhr = higher fares for the paying pax. As long as Lhr and the airlines can keep Lgw from any success in long-haul routes, they can all benefit from higher fares and changes.