I think US citizens get a bum rap. Because of something Ray pointed out. We only have two choices. If I sat down and listed 20 things I think important and my representatives could make a difference on I probably would end up with 12 fitting with policies of one party and 8 another. Might even be 50/50. I think that would be true of 80% of the voting public. But you only have two choices and politicians are adept at firing up people on a couple hot button issues and people vote for the lesser of two evils.
Except wait a minute. When did I last have two choices. Gerrymandering has become far worse in the last 30 years. My state representative for state congress is going to be a Republican Christian right wing nutter. The other party hasn't run anyone in this voting district for 18 years. In the primaries I can help choose between several nutters to determine how nutty they will go.
I have an odd, but not terribly uncommon situation with my representative to federal congress. A district was created so it would be majority black (to maintain majority white areas elsewhere). So I am in a district that is composed of 3 heavily black urban areas, but to make it a single district long thin areas run across more than 120 miles stretched more than halfway across the state I live in. Where I live I am in that district, but it is only 1.5 miles wide. My representative is going to be a black female Democrat who best represents the desires of black women on welfare. The other party sometimes run a candidate though usually not. They get about 25% of the vote.
So where exactly is my real choice.
And it is of course no surprise that politicians say one thing and do another. Most have some hot button issues like the 2nd amendment or abortion or welfare they'll abide by pretty well. Otherwise what they say and what they do about issues have no connection. Now give me a list of top donations and I can tell you how they vote. About that they are more faithful than wives are to husbands. Someone introduces a proposal to legalize marijuana or even decriminalize it? Those guys whose top contributors are what appear to be doctors groups (but are actually funded by pharma) and actual pharma associations. He's going to vote no. A party that champions worker's rights vote on a proposal to give more protection to workers, if the top donations come from large companies wanting low wages she's going to vote no. All the big corps give money to both party candidates to have access. Having only two or locally one is economical for them.
Now I think it got this way because donations from corps has been ok'd by Citizens v United. Was happening before that. That is how it ties in with the Cambridge Analytica thing. Having such info keeps current parties in a position to have the best data to manipulate things to their liking. To know how to keep people's eyes on stupid hot button issues and ignore what is really going on. I don't think CA did anything different in kind that what was done for Obama though it was more intensive. Both were wrong.
So polarizing politics with only two parties shouldn't be too surprising. The media has become polarized itself (though here by US standards the majority of the media are far more left than the general population). Look at a site like:
https://www.realclearpolitics.com/
You can just go down the articles on the home page and go: this one is leftist, this one is rightest so on and so forth just from the titles. You'll have to look hard to find centrist positions.