Yes. Because it was cheap, easy, and had everything you wanted.

As Steam Founder Gabe Newell pointed out, the issue of piracy is usually a matter of supply than anything else. People will usually take the easier option, and if piracy is that option, they'll do that.

Hence why Steam did a big number on game piracy, since you could get a game, and it would work in a few clicks. You didn't have to enter codes upon codes, or root around and install requirements from the wizard before you could start. It was basically all handled for you.