Mostly because the 9er is horribly over fueled at every point of it's stock map, I know there's a good reason for it but I don't remember why
Correction: The stock fuel map is not horribly over fueled everywhere, at least not my '02 according to my installation of a A/F sensor feeding info into a data accumulation module which gave a good indication of the stock map across a broad range of operational conditions. At normal cruise throttle settings the A/F was in the 13.2:1 to 13.6:1 range: a bit fatter than stoichiometric 14.7:1 but by no means "horrible". Once the throttle is much past 40 to 45%, however, it drops into the mid to low 9s, which I suppose is intended to keep the pistons cooler than would be the case with a leaner ratio. Obviously Honda knew the average owner isn't going to use that much throttle all that often, so what's the harm in extending the life of the engine?
The tendency to ascribe a practically maliciously rich stock map is promulgated by PCIII users that are nearly as fanatical as the Ohlins owners, invariably indicating a desire to "get as much out of the motor as I can", while in reality the actual gains are minimal at best, and sometimes shake out to losses.
Bottom line: if you are looking for an accurate map there is no substitute for a dyno run, or possibly several, done by an experienced operator who then writes a custom map for your setup. Anything else is tuning by anecdote bolstered by the ever unreliable butt dyno, and that is simply a waste of time and effort.
My advice? Run it with the stock map and see how it reacts. If it's chuffing soot and blubbering by all means lean it out some, but approach that cautiously: too lean is a great way to learn how to replace holed pistons, or worse discover how much a shop charges to do it.