It's been massively popular right across the English-speaking world for the past 30+ years ... long enough for memories of the war to have faded, perhaps?
It's oldfashioned and very seldom used among Afrikaans-speaking South Africans, but black South Africans are very traditional in their naming habits and usually prefer missionary names, so in addition to young English-speaking whites, you can meet black Sarahs of any age. I've actually never met a Jewish Sarah! Mara, yes ... born just after the war.
Some member of the Brit royal family, possibly PrincessMargaret, named her daughter Sarah a long time ago - more than 40 years - and my mother was amused at comments from people on buses, shop assistants etc that Sarah was a name for servants and therefore not suitable for royalty. She could have silenced them with a well-aimed history lesson, but chose not to!
What I have noticed is that either Sarah or Sally can be fashionable nowadays but not both. I grew up with many Sallys and no Sarahs; now it's the other way round.