It's common practice to give your child the name you intend to call him/her. Giving your child a formal name with a nickname (for example
Elisabeth "
Lisa") without the intention of ever really calling her
Elisabeth is mostly considered unnecessary. Dutch usually don't care much about formalities and would usually opt for the practical solution of just naming their daughter
Lisa as a full name. I guess this is the reason for all the nns in the top 20 :)