Not just time, but also demographics. Most issues today are urban vs rural. Urbanization tends to increase over time, moving us further on progressive topics. You can see this most clearly on gun rights in countries that hit 80% urbanization under similar representative governments.
probably going to get in trouble for this one, but it proves your point:
I was actually going for this one. There's a lot more red than blue, but there's more people under the blue area. It's pretty fragmented, especially the blue areas. So it wouldn't divide cleanly.