TL;TR: So the likely reason that time travelers from the future aren't visiting our period is (other than time travel perhaps being physically impossible) that we're just not that interesting, and we're not really that large. It's only temporal-centric egotism that makes us believe otherwise. --- Interesting answer nonetheless. Reminds me of numerous scams of people traveling from the future, including faking of very old photographs with people wearing modern Prada glasses..