They are elected by us and it's not in their interest to ruffle the feathers of those that voted them in.
The decision did not go to the planning committee, it was made under delegated authority by council officers (unelected). It could still go to appeal but I think that Lewisham's grounds for rejection are pretty solid, based in Lewisham and London planning policy rather than simply choosing the most popular course of action, and I would be quite surprised if an inspector would overturn such a decision.