Because liberal (progressive) areas are full of people who are advocating for change. What that change should actually be varies greatly between individuals, so

Because liberal (progressive) areas are full of people who are advocating for change. What that change should actually be varies greatly between individuals, so there is lots of fragmentation and in-fighting. The idea that you could vote for your specific niche but fall back to your preferred monolith is desirable because you don't feel like you're wasting your vote by voting for a minor party who will likely never win a seat. Conservative areas are full of people who want to maintain the status quo. They have varying ideas about how things should be but are unified by the fundamental idea that things shouldn't change. Since there is far less fragmentation, there is far less need to give your voice to a niche so they're happy to have their vote go directly to a monolith.