Richard Hershberger on the SABR 19cBB list:
To expand on this, the growth of baseball clubs from 1851 to 1854 went at a snail's pace. 1855 was the breakout year. The number of clubs ballooned and newspaper coverage--while modest by later standards--became for regular and more extensive. This was not coincidental. The previous December, three clubs (i.e. most of them) met and agreed upon a common set of rules. These rules were published the following spring in The Spirit of the Times. This was the first time a newspaper published any baseball rules. Over the course of the summer a virtuous cycle was established: baseball players could get their names in the paper, which encouraged more people to take up the game, while newspapers could get baseball players (and their friends and families) to buy the paper by printing the players names. This positive feedback loop led to more and more ball clubs, and more and more newspapers covering baseball.
It also established a marketing strategy that would carry the New York game across the country. A recurring pattern in many cities was that the local newspapers gave little or no coverage to local ball clubs playing the local version. (Much of what we know about these clubs comes from the New York weeklies.) Then some enterprising young ballplayer would emigrate from New York to some far flung provincial village such as St. Louis. He would bring with him the New York marketing tool kit: establish a relationship with a local newspaper editor; have the rules printed in the paper; publicize the formation of a club (or, better yet, two clubs); send game accounts (match games between the two clubs, if possible; otherwise intra-club games) to the paper. Pretty soon young men are forming new clubs in droves, and the old local version of baseball is quickly abandoned in favor of the "more scientific" "regulation" game.