Actually, as I recall it, Paizo had a two-part response. Golarion was the first part: they had to move forward on something, so they moved forward on a campaign setting. The Pathfinder rules were the second part: the GSL was horrid, so Paizo needed a ruleset.
I might be misremembering, but I clearly remember a lot of anticipation and eventual exasperation waiting for the GSL, and it basically being presented as a fait accompli by WotC, without consultation with the major 3rd party publishers, so they felt pretty blindsided by it.