Part of the reason it passed is that it was an amendment to the Telecommunications Reform Act, the biggest change in telecommunication regulation in the last 1/2 century so no matter what we did, it was bound to pass then.
Being involved in fighting it was a whole education in how Washington works and part of the reason I suspect we're going to have to continue fighting SOPA/PIPA for a long time to come, even if it's on the back burner right now.
Through a combination of people ignoring it, and the Supreme Court eventually knocking the worst part down, it wound up 'mostly harmless'.
Not every battle has to be won via a vote in the legislature.