Because in this TL communism(or its milder version: syndacalism) never developes the panoplia of simbols and iconography of our TL.Depends what you mean by "socialist". There's not exactly unity with symbolism except the colour red. Itself not purely socialist in origin.
May be hamme and sickle could be more common, but its not standard and is associated with failed russian revolution.
Red is perhaps the most common things communist states have in "La Triplice", but the flag show more a nationalist feel than a international one.