Tory vote not turning out because they know they're shit, labour vote diminished because it's been reported as a sure thing for most of the campaign, plus a general apathy towards politics in general given how bad it's been for the last 5 years.
Turnout has been dropping since 1979, arguably as the industrial base of the UK has fallen, and importantly trade union membership and active union membership was reduced and people linking politics to their actual working lives was broken
