1. Playing surfaces are shrinking. This isn't exactly true, but it is effectively true when you see how much bigger, faster and more athletic players have become. Modern athletes simply cover more area in a defined period of time than their predecessors even just a few years ago.
2. Analytics are taking over the game. With modern computing power and readily available data, it is now easy to get detailed information about even the most minute situations on the field.
Item #2 probably has a bigger effect on baseball than on any other sport, since it's the one sport where every "play" is made from a set position where the DEFENSE has control of the ball. The shift is just one aspect of this data-driven approach to the game. Another aspect is that the role of the MLB manager has basically disappeared. Computers dictate the matchups and the strategy, and the decisions are all made from an office instead of the dugout. That's why the days of the vintage "character" managers like Casey Stengel, Earl Weaver and Tommy Lasorda are over.
One of the consequences of these changes is that scoring will have a natural tendency to decline as time goes on. This is because it's easier to manage and strategize a defensive system in most sports with a bunch of players who are good athletes and are willing to work hard. Offensive production, on the other hand, usually requires exceptional talent that can't really be "coached" into a player.
The biggest and nearly ONLY reason for lower scoring in baseball if it is indeed true (I haven't noticed it at all) is:
All the damn relief pitchers entering the games inning after inning.
Every pitcher these days is told to go throw hard and as long as you can, etc.
Complete games by starters are nearly nonexistent.
Now..... almost every time a batter gets in the batter's box he's facing a DIFFERENT PITCHER.
That is BS!
“and the decisions are all made from an office instead of the dugout”
I don’t believe that.
I think that statement is conjecture and speculation, at best.