A lack of choice is more consistent with illiberalism

If the left is defined by authoritarianism and specifically economic authoritarianism then it is clear that people who hold this ideology will be less offended at a lack of democratic choice. If the left is illiberal and authoritarian there will be less difficulty for people of the left to vote for the Labour party than for the rest to vote for the Tories. It is more difficult for someone who is anti-authoritarian to vote for the Tories than it is for someone on the left to vote for Labour since a lack of choice is more consistent with economic illiberalism. And it is for this reason that first past the post elections tend to favour the left.