Be careful with your definitions. Communism, Socialism, Marxism, Leninism, (i.e. leftist) are all forms of Collectivism. Neocons are a particular breed of foreign-policy ideolgos only attributed to the "right". I can't think of a "Conservative " group that advocates collectivism.
Discussion
Because you are brainwashed to think that politics is a sliding scale instead of a spectrum.
It's ok, you're American, your entire education system and Media exist to brainwash and indoctrinate you to think like this, but you can still break free from it.
Just think for yourself instead
I dont believe "politics" is a scale, or a spectrum. Its a philosophy, backed by force. And I disagree with it.
Fascism and Nazism are both right wing ideologies.
It's worth remembering the context of where right and left arose: the French revolution.
Nobody was pushing individual liberties and free market capitalism.
The words "Fascism" and "nazism," and "socialism" and "communism" "marxism", "leninism" and "capitalism" were around before we thought in term of left/right thinking. Its an example of gross simplicity fallacy.
We need to get back to definition of terms. Leave right/left behind and let's talk philosophy. Most of the "isms" are just a rebranding of older ideas mean to enslave us. With the exception of Individualism. Individual freedom is antithetical to both the current right, and left.