Azrael360: because what they do is a steal, and nothing else.
You couldn't be more wrong seeing as piracy is NOT stealing and therefor something else, piracy falls under the category "copy-right-infringement".
Piracy is basicly like seeing a car you like, finding the schematics, and remaking an excact copy, ofcourse doing this on the internet requires no work at all, which is why it's so wide-spread.
Which is why the piracy laws and so...diffuse (very dependent on which country you live in), because copy-right-infringement for non-commercial (only private) use has for a long time been accepted as completely legal, at least in a LOT of countries.
edit: you might think the terminology is just a minor detail but i truely matters, im pirating civ4 as we speak (as i want to play a specific mod for it), now i even own the game (with both xpos) but it would be a 3 hours drive (and i have no car) to retrieve it from my home at my parents, there is therefor no copy-right-infringement at all in action here.
But if it was stealing we were speaking of, the action would still be illegal.
(it is important to note that when speaking of digital ownership, number of copies is not an issue, as it would be with physical things, in which case my product would have to include a right to duplicate for private use)