Here's why:
Since you deal with your dispatcher directly day in and day out, nobody in your company knows you better. Your dispatcher knows how many miles you like to get each week, what areas of the country you like to run, how hard working and reliable you are, how flexible you are, whether or not you'll cheat on your logbook, how often you like to be home, what types of loads and how many miles you've been getting lately, and so on.
If there is a load planner distributing the loads, that load planner likely doesn't know you or much of anything about you. Just like a dispatcher will have a group of drivers on his or her board, a load planner will likely have either a region of the country or a group of several different dispatchers that he or she is responsible for handling.
I'll give you an example of how this can work:
Say you are running regional and getting home every weekend. You like at least 2500 miles per week, you work hard, you're reliable, you've been with the company for five years, and you have a wife and three kids at home. On Monday load planner A gives you a 300 mile load from New Jersey to Pennsylvania for Tuesday. Now, on Tuesday you're in load planner B's region and you get a 200 mile run from western PA to Baltimore, MD for Wednesday delivery.
Now, on Wednesday you are in load planner C's region and you get a 180 mile run back into New Jersey. If you normally shoot for 2500 miles per week and you're running 5 days and home weekends, then you're averaging about 500 miles per day normally.
Well, here you are on sitting back in New Jersey on Thursday morning with only 680 miserable miles and you're supposed to be home in another day or two. There is no chance whatsoever you're going to have a good week this week. You may only get half the miles you were hoping for.
Why did this happen?
Why didn't you're dispatcher do anything about it?
See, in this type of system the dispatcher has less authority than the load planners. If a load planner says, “this is the way it is” then that's the way it is. Your dispatcher can not overrule the load planner. Now a good dispatcher who really cares about their drivers will beg and plead with the load planners to get you the best freight possible.
The office in this type of system is in a constant state of lobbying. Deals are being made and compromises being sought day and night. But the problem is that the load planners often times don't really care. It's not THEIR drivers who are unhappy, it's the dispatcher's drivers. Besides, their job is to move the freight efficiently within their region, not to move it in a way that makes every driver happy.
Once they move a particular driver out of their region it's not their problem anymore. Believe me I'm not making this stuff up. I've lived it. There's a reason that most companies have locks on the doors and bullet proof glass separating the drivers from the dispatchers and load planners. You think I'm kidding? I'm not.