Riding a bike is a risk, but it's a measured one based on our own perception. We're not supposed to but we make assumptions all the time.
We assume that cars don't jump lights which have been red for half a minute or more, or pull out from side roads without slowing or looking, or drive on the wrong side of the road.
It happens - we've seen it on Police, Camera, Accident! on the telly, when the cops are chasing the baddies in their nicked Vauxhall Vectras. But if we thought about it too much we wouldn't leave the house at all, never mind ride a bike. The world would be too scary.
Generally other vehicles can only do two things that may cause them to conflict with you: change speed or change direction. All you have to do is assess their options and weigh up the likelihood of either happening, then be on your way. It's that easy.
Except when there's endless queues of traffic in each direction and only a few feet, or a few inches, between you and them, that's an awful lot of thinking to do, plus pedestrians and bicycles, and cows falling from the sky* to worry about. Input, assess, act, move on - it's a conveyor belt of information. The faster you can process it, the faster you can go.
*That happened too, once.
A Russian transport plane was in trouble and needed to lose some cargo or else fall out of the sky, so the crew threw out a cow along with some other stuff. The cow landed on the bonnet of a car, which crashed. Honest.