Remember, nothing is alleged to--or can have--happened to all of MLB over some one or two seasons: the claim is that PEDs were being used at a slowly but steadily increasing rate (and thus "distorting records") from very roughly 1980 through the present. Were that so, or anything like it, we would expect to see a clear long-term uptrend during this period. But we don't: we see a nearly flat line that, if anything, slopes slightly down. The "boost" just isn't there. But that doesn't seem to stop anyone from talking about it.
Turn of the century baseball attendances were modest by later standards. The average for the 1,110 games in the 1901 season was 3,247.  However the first 20 years of the 20th century saw an unprecedented rise in the popularity of baseball. Large stadiums dedicated to the game were built for many of the larger clubs or existing grounds enlarged, including Shibe Park , home of the Philadelphia Athletics , Ebbets Field in Brooklyn , the Polo Grounds in Manhattan , Boston 's Fenway Park along with Wrigley Field and Comiskey Park in Chicago . Likewise from the Eastern League to the small developing leagues in the West, and the rising Negro Leagues professional baseball was being played all across the country. Average major league attendances reached a pre World War I peak of 5,836 in 1909, before falling back during the war. Where there weren't professional teams, there were semi-pro teams, traveling teams barnstorming , company clubs and amateur men's leagues. In the days before television, if you wanted to see a game, you had to go to the game.