One need not have ever personally used a floppy disk in order to recognize the symbol and pick up its meaning through cultural context; this is exactly how we learn to associate meanings with most of the symbols we use. We gain familiarity with all kinds of obsolete technologies throughout the course of an ordinary education, and easily recognize images of such devices whether or not we've ever seen one in real life - but beyond that, we learn to recognize all kinds of completely abstract symbols and use them as comfortably as words or numbers. There's nothing harmful about the fact that the "save" icon happens to look like an obsolete bit of storage media; the "save" symbol could have any shape, as long as it doesn't already represent something else.

Of course it's possible to pick a different symbol to represent the action of saving data to permanent storage: but why bother? We have a symbol, and it's as good as any other arbitrary symbol might be. Changing it would create confusion for no benefit, since it's ultimately the association of the symbol with the action that matters, and not the history of that symbol's origin.