Comment by bodiekane
I think you're taking the graph way too literally.
The Republicans and Democrats are both coalitions made up of many different groups, and their policies are constantly shifting depending on which individuals get elected and which of those sub-groups hold more power, as well as due to different sub-groups shifting allegiances.
It's statistically almost impossible that someone would agree 100% with the platform of the Republicans or Democrats at any given moment. Even if you just pretend there are exactly two stances on a given issue (R or D) you'd still be looking at like 2^1000 different possible outcomes (for 1,000 different issues). The more perfectly someone claims to align to one party, the more likely it is that they're doing so out of tribalism than because they actually matched the exact one-in-a-zillion set of opinions.
The graph isn't "agrees with Republican" and "agrees with Democrat" as the axis (I also would say you can agree with people and still be a free thinker, viewing positions as independent doesn't really make sense, there's underlying ideology that heavily correlates them but all of this is besides the point). The idea that the far left is agreeing dogmatically with the democratic platform is clearly factually incorrect to anyone who has met people actually on the far left (they rarely even agree with other people on the far left) and a similar thing can be said about the far right.
The really obvious example of this is look how much of a thorn in the side of the Republican Congressional leadership the far right has been. Agreeing rigidly with a party will not put you at the edge of the graphs at all (for most parties globally it would put you somewhere in the middle)