I suspect there are two factors involved. First, in the old, old days, socialists who advocated local socialism (as opposed to international socialism) and who did not advocate violent revolution were called right wing. They were right wing only when compared to other socialists and communists who were advocating international socialism and revolution. Here is a speech of Lenin's where he refers to subgroups of the socialists as right wing: Lenin 1920 Speech.
The second aspect of this is that the left wants to foist Hitler off as somehow connected with conservatives or the right wing of American politics. The media play right along with this line. They continue the old right wing definition of Lenin. However, some of today's neo-Nazi groups advocate some of the same 'nationalize big corporations' goals that Hitler wrote into the Twenty Five Points of the Nazi Party. Hitler's Nazis were clearly socialists and left wing by American definitions of the term.
The Nazis weren't called 'National' Socialists for no reason. They were German 'national' socialists as opposed to German 'international' socialists.
"Comrades, the bourgeois press of Germany and France is devoting much attention to the discussion within the German Independent Social-Democratic Party and the Socialist Party of France on affiliation to the Communist International. It is vigorously supporting the views of the Right-wing opportunist sections in the two parties..."
Cordially,