Because different folks define those differently.
A democratic socialist is very different from what most people think of when they hear communist.
Also I'm very left leaning but still like some aspects of capitalism. It just needs to be regulated or else monopolies eat everything and turn capitalism into feudalism.
These good Mormon boys have wrapped your answer up in a nice little song
https://m.youtube.com/watch?v=mKB_W4Fv_vY