I agree with all the below AND
Many people like the nicknames
Ollie or
Liv.
Ophelia has no obvious nickname.
Ophelia's story in
Hamlet is tragic.
Olivia in Twelfth Night is less well known and comic.
Olivia has nostalgic links to figures such as
Olivia Newton John.
Olivia is known and used in lots of languages.
I like
Ophelia and know 2 little girls with the name, but I am not surprised
Olivia is more popular.