Classic girls' names tend to come with generations of history and a rich set of nicknames. Elizabeth gives you Betty, Eliza, Beth or Liza. Margaret gives you Maggie, Meg, Daisy or Peggy. That optionality is part of why these names never truly fade.
Timeless rather than trendy
A classic name sits outside the charts. It rarely spikes, and it rarely disappears. Alice, Grace, Anna, Clara and Hannah have all stayed in gentle rotation for well over a hundred years. That is exactly the profile parents often want.
Room to grow
A classic gives a child room to be formal or casual. Eleanor can be Nell at home and Eleanor on a letter of acceptance. Margaret can be Maggie now and Margaret later. That adaptability is one of the quiet gifts of a classic name.