Triples have become somewhat rare in Major League Baseball. It often requires a ball hit to a distant part of the field, or the ball taking an unusual bounce in the outfield. It also usually means that the batter hit the ball solidly, and be a speedy runner. (The inside-the-park home run is much rarer than a triple). The trend for modern ballparks is to have smaller outfields (often increasing the number of home runs); it has ensured that the career and season triples leaders mostly consist of those who played early in Major League Baseball history, generally in the dead-ball era.
The triple is considered one of the most exciting plays in baseball. A triple is the hardest to achieve in terms of hitting for the cycle (a home run does not have to be "inside the park" to count towards the cycle).