As long as you buy a modern dually truck you will be able to handle the camper. If you are trying to get away with a SRW truck then you can't handle it. The actual weight varying a few hundred pounds won't change that reality.
As for why? With a TC and the right truck you can basically have a small, 4wd, diesel powered motor home with an incredible tow rating. You can tow a 8,000 pound boat to the lake, set up your camper, then take the truck out from under it to launch and retrieve the boat. Name another RV that can do all that.
And, if you already need to own a truck for other purposes a TC is much cheaper than a MH.