Should one of the parties also support slavery just so that you have a choice? Eventually an issue reaches a point where the vast majority of the population supports an issue (such as keeping slavery illegal), and when that happens it shouldn't be a surprise that no parties are against it. I hope and think this is what has happened to the issue of same-sex marriage in the UK.
Where 'vast majority' can equal 55%. Or not even then - sometimes an issue is not worth fighting over compared to others. Most people want to pay less tax, for example, but politicians of all stripes know that's not feasible, and stick with the minority desire to keep taxes up and focus on other things.
Another thing that politicians are great at ignoring is the general public's disdain for their paypackets. On this issue, even the most brazen shouter of 'my mandate comes from the people' turns to 'this is a delicate issue that the public don't understand'...
