The reason people read slowly is because while reading they try to pronounciate every word. Even if you don´t read out loud the vocal cords are moving as if you were speaking. This comes from when we learned to read as children by slowly pronounciating every syllable out loud, mainly so the teacher could hear that it was correctly read. The vocal cords are controlled by muscles and muscles can only move so fast, so this has to stop if you want to read faster.
Also the eye movement has to change. There are certain eye movement techniques that increase the ability to see text differently than most people do today while reading, scanning actually instead of reading.
So if you want to read faster, get on with it! We have learned the wrong way to read, it´s time to correct it.