Janu, it is not what you think. IMHO: When we read something like the Quran we recite it aloud or internally. The tilawaat is not just reading what’s written but to sound it out in a singing manner as it pleases Allah (sbwt). With that, the body also sways, it’s rhythmic. It is unconscious most of the time. But the movement helps in getting the person to focus more and longer on recitation.
I believe it would be hard to stay still while reciting. Remember, we don’t read but recite and there’s a difference as I tried to explain above.