I think this is done to save processing power, soncidering it would probably take a lot of memory to render all binary stars in the sky seperately; so if they are rendered as a single star (the barycentre) until you come close, it is a lot less work for the program. Though I do think the distance at which the program stops making the barycentre a star (0.01 pc) is too small and should probably be increased tenfold so the cases where we can actually see the barycentre star seperately are very few.