Popular song reflects the attitudes prevalent at the time it was made. A very simple answer; but then, I don't really see the point of asking the question. An equivalent question might be, "Why does Shakespeare use so many old-fashioned words?" The answers lie in the context of the material, to which the political and social attitudes that prevail today are irrelevant.

If, on the other hand, you were to ask why these things still appeal to us now, there would be some scope for useful discussion, perhaps; but even then I doubt if there would be much to say that hasn't already been quite well covered.