The comparison to business plans is silly. Businesses compete for a limited number of consumer dollars in particular marketplaces. They have to respond to each others' actions directly. Knowing what someone else is doing in many cases tells you exactly what you should be doing. If you know someone's business plan, you know when to release products, how much to invest in advertising and where, etc.
In running, you might argue that you can learn whether someone is peaking or training through, and adjust your own training accordingly. You might figure out before a race whether someone is in shape and adjust your tactics. But realistically, these are edge cases. You know that people are trying to peak for the trials and hold it unless they're so good they don't need to. Sure, people like to win during the rest of the year, but they're not likely to make any major adjustments to respond to their competitors just for a road racing season. But even if some degree of secrecy is a concern, it's not a binary, share-or-don't-share trade off. You could opt to selectively release workouts during key times of the year in order to maintain secrecy, while still sharing 90% of what you do.
In any event, I think runners are missing a huge chance to develop a bigger following, particularly among recreational athletes who don't follow the pro sport.