J. C. Bradbury's book, "The Baseball Economist" is a must read for students who like baseball, economics and statistics. He offers the hypothesis that baseball expansion is another explanation for the spike in home runs between 1998 and 2001 than steroids use. Roger Maris hit 61 home runs in 1961 when the Los Angeles Angels and Washington Senators joined the American League. His second highest home run total was 39. Baseball expanded prior to the spike in 1993 and 1998. The causal relationship is that as the league expands, talent becomes more dispersed. On average, the best hitters face worse pitching, and vice versa. Bradbury writes,
What does this say about the current ear of baseball history, especially given the intense public focus on steroids as the cause of the increased number of home runs? Pitching talent is more dispersed than it has ever been, while hitting talent is still quite concentrated. It means there are plenty of batters out there who are able to take advantage of bad pitchers. A more dispersed pitching talent pool gives the best hitters greater opportunities against weaker talent, which ought to lead them to perform extreme feats...Bradbury concludes,
Also, if low-quality pitchers are hitting more batters, shouldn't better pitchers benefit from facing more bad hitters as hitting talent has become less compressed since the 1980s? In fact, they do, as pitchers increased their strikeout rates over the same span....
The fact that talent dilution may be part of the cause for the great performances of players does not mean that steroids have not influenced the game. However, it's certainly incorrect to say that steroids, or other performance-enhancing drugs, are the only explanation.