If you haven't realized it, offense has been going down for the last two years. Last season was the beginning, but this season has really shown a much greater decrease. The number of shutouts in the game is up -- if the current trend holds there will be 338 Shutouts this season. By comparison, in 1999 there were 193 shut outs. Baseball is on track to have its worst offensive season since 1972, which was the year that caused the American League to implement the Designated Hitter.
These are simply the facts -- the question is, why is this the case? Personally, I don't think there is any one reason, and it is difficult to say what reason is having the greatest effect. However, I can still list the contributing factors and why I think they are contributing.
1. The end of the "Steroid Era".
This seems to be the most commonly cited reason for the offensive deflation, and it seems likely that it certainly plays a role. PED testing has become widespread, and players have been suspended who don't conform to these new rules (see: Manny Ramirez). However, while the apparent purification of the game has certainly had an effect, it is difficult to say that it is the only one.
2. Pitchers are getting better.
Of course, it's hard to say this since the statistics that a pitcher has are clearly effected by the caliber of hitting in his day and age, so the main thing that I'm going to use in my discussion of this is the average miles per hour of fastballs for major league hitters, as it is something that is static and is not affected by the pitcher's environment. According to data gathered by Bill James, the average fastball speed the lat few years is as follows:
Obviously there is a trend developing here. You probably could have figured it out without looking at the numbers simply by thinkign about the number of young pitchers who are around right now who throw extremely hard: i.e, David Price, Daniel Bard, Joel Hanrahan, Stephen Strasburg, etc.,
In short, I think the caliber of pitchers right now certainly plays a role in the loss of offense.
3. Failure of hitters to adjust their philosophies
Baseball players today strike out a lot. That's no secret. Personally, I believe it to be a remnant of the so-called "steroid era" in that players did not mind striking out so much because offense was so easy to come by, so an all or nothing approach was efficient. Now, with offense coming at a premium, and players hitting fewer home runs, players have failed to change their strategy. Players are still striking out a lot but are not supplying the power necessary to make their strikeouts worth it. There are of course players who are exceptions to this such as Adam Dunn and Ryan Howard, but there are many other players who should probably change their approach (See: James Loney, Mark Reynolds).
4. More emphasis on defense.
I've talked about the increased emphasis on defense by General Managers on this blog before, this emphasis is a product of General Managers adjusting to the of the steroid era. In general, the fact that more and more General Managers have become more interested in players who can provide solid defense and hit, there are simply more guys on the field who can effectively play both sides of the ball and fewer hulking outfielders and first basemen. This is more certainly a contributing factor to the decrease in offense.
Anyway, that's it for now. Let me know if you have any other ideas as to why offense has decreased.