Vultures... I mean realtors

We had our condo on the market for almost a month. In the "hot" Vancouver market we thought it would sell for sure. It didn't, but that's okay; we arranged the swap, which allows us to keep our place - which we love. As soon as we delisted, realtors started mailing and calling (how did they get our number?). They all start with, "I see you've recently been trying to sell your house." One even said she had several people interested. Where were they when it was on the market? Is there a whole subsector of realtors that wait for places to be delisted? I don't get it. I do get the calls and letters, though.