I ride a motorcycle. Even a 5 mph bump from behind can cause serious damage/injury. Cyclists are taught that when someone tailgates you, you should slow down because you need to make sure they have enough room to stop, and the closer they are, the slower you should go.
Others made valid points about keeping right and I’ll go one further. If you’re in the left lane and barely passing the cars to the right, you don’t belong there. Imagine the other cars are parked - 0 mph - then estimate how fast you’re going in relation to them…it’s often not more than 1-2 mph faster. It’s not enough to justify blocking passing lanes, please be considerate and move over. Likewise, if there’s open road in front of you, and cars behind you, no matter how fast you’re going, please move over, it’s not your job to be a pace setter and you’re encouraging tailgating and passing on the right.