It is generally believed that the decline in voter turn-out since the 1960s has been due to several factors.
People increasingly feel that their single vote among so many cannot have any effect.
There's a feeling that all politicians are the same under the skin, so what's the point?
Apathy - life is hard, and I have too much on my plate to bother with getting out and voting.
Interestingly, non-voting has increased the most among people who started voting after 1960.
This subject tends, inevitably, to bring up the question of proportionate representation.
In countries where voting is mandatory turnout figures do tend to be higher, but it's difficult to come to hard and fast conclusions about its benefit. A true democracy is about freedom of choice, and whether to vote or not must surely be a matter for each person to decide.