For one, it's spring and that's when many sellers put their home on the market thinking it's the best time to sell. And you may also be noticing builders' home listings which are basically ads for new construction homes.
Another reason is that Stone Ridge is a fairly new community meaning that many people who bought in the community have not come to the "5 year" mark - the average number of years people in the DC metro area live in their home before moving once again. As the community matures, you'll see more people selling (and buying).
And you may have the new car syndrome - when you buy a new car, you seem to notice the same type of car everywhere you go even though you didn't notice it much before you bought it.