It was probably hard to find because for some strange reason LEGO aren't supporting the PC as much. The Pirates of the Carribean game didn't get a big retail release for PC (As you noted on the page for it) and a limited online presence. Going by how bad the ports are (I have LEGO Star Wars Complete) I suspect it's a financial decision.
It's nothing to do with turning it into an online game, though (Which would be LucasArts' decision I suppose), as with LEGO Universe, Clone Wars Adventures, Star Wars Galaxy/Galaxies and the upcoming The Old Republic it'd be pointless. Everyone involved would be shooting themselves in the foot rather literally if that were to happen.