WOTC at least has an excuse, though not a strong one. Hasbro has strong equal competition, and the competition gets useful data out of knowing what their production runs are for the Christmas retail season, to judge shelf space available. So, Hasbro as a corporation has a policy to not release said data, and that filters down to WOTC. So while it's not a great reason for WOTC's perspective, at least "our corporate masters tell us to do this, and they have decent reasons even if they are not directly applicable to us" is an understandable one.
Paizo does not have that same concern. Maybe they have other concerns, but I don't know what they might be for this particular data point.
What competition would that be, and how would this data help the competition or hurt Paizo in any way?
Seriously, can anyone spell out a hypothetical situation where knowing the print run of the first run of Pathfinder would meaningfully help the competition or hurt Paizo?
As for those folks complaining about my asking - why? I congratulate Paizo on selling out, and I am happy they are doing well. Asking what the print run is should not take away from that. Why are you so bothered about people wanting to know the print run?
I don't think that it's down to Hasbro. I don't remember TSR or pre-Hasbro WotC releasing sales numbers with any regularity (off-hand, I can't remember any timely official releases of sales numbers; what I've seen has been more like "over X" and that coming some time after). It seems to me that all business have interest in keeping those numbers to themselves, because they are in a competitive market and any sales numbers are information that competitors would want to know.