As more teams and pitchers embrace things like spin rate and Edgertronic cameras, we’re seeing more and more high fastballs. Part of this is a response to the fly ball revolution which caused hitters to swing slightly up. Every pitch comes across the strike zone at a slightly downward angle, so pitches lower in the strike zone tend to get punished by the uppercut swings because the path of the pitch aligns with the path of the bat. Higher spin allows a pitch to resist gravity better which in turn, keeps it off the bat path.
Low fastballs are getting crushed, but high fastballs are reigning supreme.