Because in many countries at various times you couldn’t be taken seriously by the bulk of working people if you didn’t call yourself a socialist or at least attach a “social” label to your beliefs like “social-democratic,” “social-liberal,” “social-conservative,” “social market,” “social teaching,” or “social justice,” to say that you’re not just a standard right-winger, you’re a right-winger who fights against the degenerates or the traitors or the elites or ethnic minorities or whatever for material gains for the working classes. Fascism, corporatism, national socialism, social liberalism/conservatism/democracy, etc. exist to provide a vehicle for capitalist-bought politicians to channel revolutionary energy towards what at least in theory is supposed to be a more stable capitalist order.