Susan is one of a group of girls names which are found (in some form) all over Europe - Mary, Jane, Elizabeth, Anne, Margaret, Catherine, Helen, Susan, Alice, Sarah, Isobel. Eleanor.
Other European girls names are versions of boys names -Alexandra, Charlotte, Willma, Roberta, Nichola, Andrea, Henrietta, Davina, Georgina, Martina
Then there are names which go in and out of fashion and become very dated, perhaps because of a famous singer-ot actress- Valerie, Marilyn, Gloria, Natalie, Tracey, Britney, Lola, Shirley, Kim, Tiffany.
One of my children has a name which was almost unheard of when she was born in the 1970s and is now one of the most popular. I don't know why. She is not famous!