If there are time travelers, why haven't I seen any lately?
This is a timeless question, and barring the problem with using such tenses as present perfect and time-markers, such as "lately," it is at the heart of most people's misconceptions about time travel. But before answering let me elaborate on the question.

The non-time-traveler: makes the assumption that if time traveler were possible, there would certainly have been time travelers seen before now, which makes two assumptions:
1) That there is one time line.
2) That time travelers can be seen.
3) That none of them have been seen.
Also, implicit in this suggestion is the idea that time travelers would, if they traveled, make themselves so conspicuous that they could hardly be kept out of history books.

Without going into the problem of history books in general, let me deal with a few of these assumptions.