I think its a combination. ESPN had an amazing article here: https://www.espn.com/mlb/story/_/id/31454952/how-k-became-most-destructive-letter-major-league-baseball
In this article they break down how the game has changed. Tim Kirkjian (author), Reggie Jackson, Mark Teixeira, Nolan Ryan, and Ryan Zimmerman all break down how the game has changed. They go on saying that the game has changed by teams using more analytics than ever before. Also, stated in the article are that pitchers really don't know how "pitch" properly.
Stated in the article is also that hitters don't have multiple swings, depending on the count they have. They only have one swing. A swing that sends the ball well over 400 ft. A swing that is being hindered by the players not developing into a multi-faceted player. A swing that is only used for one thing: Money. It is widely thought that if you aren't hitting HR's and getting a ton of RBI's, you aren't winning games, which in turn means you aren't getting paid. The whole analytics aspect of hitting has forced hitter to become too predictable and only caring about hitting HR's. Which has helped pitchers out tremendously. All the pitchers have to do is avoid the hitters swing path that they have worked on over and over again, they will strike the hitter out. This is why you see players with 3-4 K's every other game. Look at Sano, Garver and Jeffers, just to point out a few, strike out rate. At one point the 3 of them were striking out at almost 50% of their AB's. In today's game a strike out is seen just as a regular out. Strike outs are seen as its better than hitting into a DP, which sometimes it is, but that shouldn't be the mentality the player goes into the AB with.
As a Twins fan, we are seeing this day-in and day-out. The Twins are one of the worst at leaving runners on base. Usually that does correlate into a horrible avg. w/ RISP. Because they have the mentality of the Bomba Squad, the players believe that they need to hit HR's to score.