I ride. And drive in London. I see more shocking, illegal, unsafe and downright stupid riding than I do driving. Honestly, some people have a) no knowledge of the rules of the road b) no knowledge of the techniques for riding in traffic c) no sense of their own vulnerability or d)ability to assess risk.
Sadly I'm with the OP. When I ride to work I'm usually the only cyclist sitting at the ASL, all the others have gone through. And they all filter on the left, clearly not knowing that the driver has no chance of seeing them. Woefully poor observation, signalling and lighting.
Problem is, I think, that so many are new or don't classify themselves as cyclists. So they don't understand how to ride, don't feel enough of a responsibility to the cycling community to ride legally and don't drive and so have no understanding of the drivers' challenge in spotting them.
There's a lot of work to be done IMHO