To clarify the "pitch to contact" point: I think of a "pitch to contact" pitcher as a ground ball pitcher. Often a sinker-ball pitcher. I doubt that number of time through the order helps a batter if he can't lift the ball out of the infield.
On "park neutrality", it seems likely that parks have closer fences because fans expect to see home runs, and the evening sports shows almost always center on who "went yard" or took a pitcher "deep" or whatever term is popular. That would explain why Nats Park might have fewer triples...and, if I'm right, why there would be fewer triples overall.
Until about 1954, Griffith Stadium had such deep fences that few homeruns were hit into the seats (in left. Center was so far that the few himers there are marked out and remembered; the RF wall was so high that many drives bounced off the wall, but would have been homers in, say Detroit.). About 1933, a CF was traded to the Nats. He said something like: I'm happy to go to Washington becvause I won't have to worry about hitting the wall.
Check the Washington all-time list for doubles and triples. I think the only current player who makes the list is Ryan Zimmerman, who is far down the doubles list, below Sam Rice, Joe Judge, Mickey Vernon, and others.
Now it seems like a batter gets a triple only when the ball takes an odd bounce in a corner.