As I've spent the last couple days flying in/out of LHR, I was wondering why the satellite T5 terminals, especially T5B is so much shorter in length, but have very long jetties sticking out at opposite ends to the building - my Hong Kong flights was on one of those gates with long jetties. Surely this can't age well and think there must be a reason for this?

I know they tend to serve jumbo jets but that doesn't fully explain why the building is shorter.

T5C looks slightly longer than T5B or is that an optical illusion? I didn't get near it during taxiing so it is difficult to tell.