You should post a better-worded version of this question to s/DebateAltRight. "Alt-Right" is kind of a dirty word now but basically means "any race-aware conservative white person" but leftist is more derogatory. The people you want to answer this question usually self-identify as "liberal" (or maybe SocDem). Leftists are like psychologically damaged people that could never be expected to accept and alt-right position (like antifa). We do see some white shitlibs (the former) convert, usually they cite race and IQ, race and crime, or heritability of political views for reasons why they switched.

Also, Alt-Right is more open to traditionally left-leaning welfare policies like Nordic Socialism. Often with the stipulation that this equation needs to be balanced with eugenics (and that the given society is entirely or mostly white, which goes without saying)