No, loads of girls' names don't end in 'a', it's just that the current fashion is for feminine-sounding names, so they (and the 'y/ie' names) seem more prevalent.
A generation or more ago it was all consonant and/or consonant-sounding endings...
Susan, Nicole, Karen, Joanne, Leanne, Helen, Janine, Denise, all the -een ending names, Maureen, Doreen, Charleen, Kathleen, etc. And also Megan, Rosalind, Cecile, Colette, Catherine/Katherine/Kathryn, Elizabeth type names.
And further back - Margaret, Miriam, Beryl, Cheryl, Ann, Grace, Isobel, Jean/ne,
June, Joan, Gertrude, Agnes, Millicent, Winifred, etc, etc, etc...