Only because they refuse the truth. Yesterday, there may have been a distinction. Today it's gone.
Liberals and socialists are both headed towards the same finsh line—government control. In the past, the distinction was about velocity; libs were headed there comparitively slowly, while socialists were in a hurry. It’s kind of like the difference between getting drunk over the course of an evening by sipping wine, as compared to knocking down several boilermakers in a row, and getting there quickly. Just as with drinking, the distinction is becoming blurry.