1) You do not need to change lanes to avoid cars at on-ramps or cars on the shoulder
2) You do not need to switch lanes to pass slow traffic (semi trucks, etc.)
3) There is more room to maneuver in case of emergency
1 and 2) So everyone should have to change lanes to get around you, but you shouldn't have to change lanes for anything?
3) Typical 3 lane highways have 4 actual lanes, the right most one being the breakdown lanes and can be used in an emergency. That means being in the middle lane gives you one lane to your left and two to your right, vs. one to your right and two to your left. Same difference, no added benefit.