I would hazard a guess that a large proportion of those that did not vote were in their mid 50s and, rightly or wrongly, decided that the proposals would have little or no effect on their retirement. You could argue that they were right to abstain from a proposal that will not effect them.
The Union has been less than honest with us during the briefings. At the briefing I attended they gave a list assurances that would be included in the MoU, giving the impression it was just a matter crossing the ts and signing; yet in their correspondence today it all seems a lot less certain and appears to need a significant amount of consultation. However, I still think a yes vote was the right one.