We were offered a choice of the existing FPTP system being pushed by both of the largest parties who have the most to lose from a change and backed up by a not insignificant amount of negative media coverage of PR.
They Yes camp was mainly being championed by Nick Clegg... who was already effectively a dead duck because of his failure over Tuition Fees and also the fact that the PR system on offer (not clear quite how that decision was made but I'm guessing the Tories made the selection) is probably one of the worst options from those available. Plus a significant tranche of, particularly the newspapers, really got stuck in on portraying PR are so horribly complex and somehow unfair that nobody in their right mind would want it in the first place.