It's not surprising. Elsa has a similar sound and feel to many of the top names (think Ella, Emma and the like), and it's actually a variant of top 10 name Elizabeth, it's not a big stretch to go in this direction.
Only poor Olaf still isn't making an impression (what does a snowman have to do to get some love?).
If you like that Scandinavian vibe but don't want to be so literal (or have your daughter be one of several Elsas)?
For BoysAnders-Andrew with Scandinavian flavorErik-A variant spelling of EricSoren-a popular Scandinavian name with famed philosopher Kierkegaard
For GirlsAgneta-The Scandinavian version of Agnes (Agnetha was one of the members of ABBA)Annika-A variant of Anna (and a sneaky way to still pay homage to the scrappy little sister)Lilya-A variation of Lily