I think for some of the parents, they either don't like the full form, or they think the full name is too cumbersome. Although in some cases, there are people who think 'if I'm going to call my son
Ben, I may as well put
Ben on the birth certificate'.
As I believe I've mentioned before, my cousin in the UK has boys called
Alfie and
Archie, as for her
Alfred and
Archibald (with
Archibald in particular) being 'too posh' or 'too snooty' for her.
Her best friend has four children;
Ben,
Sam,
Maddie and
Tom, and she is one of those who didn't see the point of putting the full names on the birth certificate when she only planned to refer to them as
Ben,
Sam,
Maddie and
Tom. Of course, everyone
assumes they are really
Benjamin,
Samuel, Madeleine/Madison and
Thomas, so much so the last time I saw her friend, she admitted it made her wish she had used the full names (so she didn't have to keep correcting people).