Maybe it isn’t. The right and left are split into different primary interests. On the right there are social and fiscal conservatives. On the left are gays and lesbians and other variations, minority interests, and feminists. But there is a common thread that differentiates the left and the right. The right are civilized, the left are not.
Look at how the left behaves, they bit off fingers, assault vendors and street preachers, and generally cause mayhem wherever they go. That’s why a group of leftists is more likely to get its way than a right wing demonstration. People are afraid of what the left will do if they don’t get their way. Heck, they cause trouble when they do get their way. The right makes a point of being civil, which is why nobody gives in to them. What’s there to worry about with a collection of conservatives congregating outside a capitol? You can pass legislation inside and walk right past them when you’re done. You’ll live to vote on more crap the next day.
Perhaps it’s not so much left and right as a gradual destruction of civilization. Nothing seems to upset the left more than people adhering to institutions the country was founded on. Religion, the family, freedom to work the land, gun ownership, it’s all under relentless attack on whatever premise is convenient at the moment. That seems to be a constant, like the speed of light.