You think the membership (at least a significant part of it) is not apathetic? So why could almost 40% of them not be a**ed to even return a postal ballot regarding pensions?
I know of former course mates that still get their union mail delivered to somewhere in Bournemouth, addresses are not up to date etc etc. I wouldn't be surprised if a lot of the ballot papers never even got to the members in first place.
I know it seems such a stupid reason but it does happen..