Apathy and abstention
The current system doesn't have a reliable way or even attempt to capture the difference between 'can't be arsed' and 'none of the above'.
If they want to spend their time doing something useful, they need to work out whether it is an issue of people not being bothered to vote, not having anyone they want to vote for or not feeling like their vote counts (e.g. being stuck in a 'safe seat')