why? what do you get out of it?, and who cares, the sooner they are on their way, the safer you will be.
Lets say I stop on the left allowing the car to pull alongside. I'm still not clear why the car drivers journey is more important than mine but lets ignore that for the moment. So we're both stopped, the driver is concious (hopefully) that there's a live person next to them. It's now time to go. The driver will do one of two things in my experience. Either floor it (that's safe isn't it?), or in a fit of rage/panic/indecisiveness, squash me against the kerb/railings. With me in front of them, they *have* to wait and therefore don't do anything stupid like kill me. If you're unclear on how dangerous this situation is then might I suggest you read up on the statistics for cyclists killed, London, 2013. You'll find a great many occur at lights as they change to green.
What do I get out of it? I get moving and up to speed, get myself into a safe position of my choosing and have control of my part of the road. Just like the driver does.
Who cares? Hmmm, well everyone really. I certainly don't fancy getting squashed, I'm sure it'll really piss my family off, It'll upset the person whose car I happen to be jammed under and what about all the people stuck in a queue behind my fatal accident?
The sooner they are on their way? You realise there's more than one car on the road don't you? Once the car immediately behind you passes, there's another one right behind it.
The point is that car drivers take ownership of the road when they're driving along. It's a standard part of driving and it's actually safer for drivers to do so. Bus drivers do it, lorry drivers do it, milk float drivers do it. And no-one complains but if a cyclist does it it's a major issue?
Plus presumably this is in London so the cyclist is going to be moving faster than cars on average anyway. It's a waste of time overtaking him because he'll pass you back shortly.