Steve Sailer points out that the young golfers leading at the US Open aften 3 rounds are all "Generation Ǝn," that is, their names all end in that schwa-n sound: Jordan, Jason, Dustin, Brandon. Add in the rhyming Braydon, Jaydon, Graydon, Hayden, Peyton, and even Creighton; plus Justin, Ethan...it goes on forever among guys born in the 80's and beyond. There are girls' names that have that ending, but I think all are ones stolen from the boys, such at Jordan, Jaydon. Madison is a tweener - the "o" is pronounced ins some versions, not in others. But recently the -a names have dominated among the girls: Sophia, Emma, Isabella, Olivia, Alexa, Michaela, Sarah, Hannah. In the previous two generations the "-ee" sound was far more popular at the end: Kelly, Tracy, Dorothy, Shelly, Amy, Brittany, and even the -a names would become -ee names in nickname, such as Theresa/Terri, Barbara/Barbie, Rebecca/Becky.
The -Ǝn sound is not a common universal for boys' names, as far as I can tell. In fact, the -ee sound that girls used was a common ending for boys' names until recently: Kelly, Shirley, Leslie, Tracy, Terry, Jackie, Bobby. The -a sound, not so much for boys. But the -a ending is a feminine ending in many languages in the world, common enough that Merritt Ruhlen and the other linguists who believe we can detect echoes from the original language of humans suggest that -a is one of the language universals that has been there for 50,000 years. Those of you who know foreign languages might reflect on whether that sound is feminine in the ones you know.
So mothers are reverting to so some deep association of -a with girl children that is old-fashioned in about as complete a sense as one can imagine. Why the schwa-n sound for boys comes from I don't know.