Laura Wattenberg, author of The Baby Name Wizard, explains why in The Washington Post: "We may like the idea of distinctive names, but our tastes are as alike as they ever were. Even parents with different name sensibilities are influenced by the same underlying name fashions: Vowels, especially long vowels, are good--think Owen and Ava. The -n ending is also good, as in Kaitlyn and Mason. But clusters of consonant sounds are bad. (Sorry, Gertrude and Herman.)"
As a result, "when the irresistible desire to be different meets immovably similar tastes," strange things happen:
You end up with those six names that rhyme with Aidan in the top 100 names of the 2000s, and 38 of them, from Aaden to Zayden, in the top 1,000. The irony is that classic English names such as George and Edward, Margaret and Alice -- the names that used to be standard-bearers -- all have distinctive sounds. They aren't prisoners to phonetic fashion; each of them sounds instantly recognizable. Contemporary names, by contrast, travel in phonetic packs. More than a third of American boys now receive a name ending in the letter N. (In decades past, the most popular boys' names were more evenly split between a number of endings, including D, L, S and Y.)
Wattenberg calls this "lockstep individualism." Those poor parents: "Instead of a classroom with two Williams and two Jameses, today we have one Aydin, one Jaden, one Braedon and one Zayden--not to mention a Payton, a Nathan and a Kaydence. In our rush to bless our children with uniqueness, we've created a generation that sounds more alike than ever."