People are gonna keep slowing down in lanes where you turn off. If they don't slow down they'd cause an accident, and if everyone travelled the slower speed, there wouldn't be any need for highways. They'd just be main streets.
You need the zoom zoom lane to get to where you need to faster. You need to drive carefully in the other to avoid running into the slowing/turning truck in front of you or to turn safetly while avoiding the one coming from behind.