My theory is a group motivated to change the status quo is far more likely to be mobilised to vote on that issue than a group in favour of maintaining the status quo, i.e. being forced to respond to that group. Because you're trying mobilise a group to do nothing, there's no impetus to the counter-movement. I think any vote like that is naturally biased towards the group seeking to change something, though it would be hard to quantify the extent of the effect and would only apply to specific single issue votes. I said this during the lead up to the Brexit vote, that more people in the country would prefer to stay, but the "leave" voter base would be over-represented at the ballot. I think the whole democratic system fails to function unless everyone is compelled to vote, because of weird effects like this.