I think the problem is that none of them are close to either 66 or the Toll Road and you can't see them from the road. It isn't like you're on 70 coming through MD and there is a sign with gas/food/lodging at each exit.
For the record....
Exit at Centerville Rd - north and south there are drive through places. If you go south, in the Shoppers Food Warehouse shopping center is a drive thru Starbucks. Head north and you will hit Taco Bell and Wendys on the left. This is the first exit past 28 when you leave the airport. Chick Fil A is in front of Target in Reston - you would exit at FFX Cty Parkway, turn left then you will see Target on the right - get on Sunset Hills and CFA is on the left.
Other than that, the closer you get to the beltway, the farther away from the freeways the food gets. I've made that drive and there isn't anything else until you get on 95 and are pretty close to the airport. I can only assume it's due to space and traffic.
Do you have a smartphone with like google maps or something? Use it - it has saved my life on more than one occasion.
The Starbucks in Greenbriar shopping center on Rte 50 just added a drive through, I was just there today.

Just look for the giant hole in the ground where McDonalds used to be and you'll find it.
What's the deal with McDonalds in the Pan Am shopping center NOT having a drive through? It isn't like space is tight in that giant parking lot that is rarely filled?