Because our Medival Ancestors are wierd!Sicerriously though, They like playing with sylables. Like Ned is a nn for Edward.Correct me if I'm wrong-which I'm pretty sure I am! :)
Ned...is from 'mine Edward' (mine being a common term of address around the 1600s/1700s, a bit like 'my dear Edward' today) becoming 'mine Ed' and then 'my Ned'. The same for Nan (Anne), Nell (Ellen, ELeanor), Noll (Oliver), Nab (Abraham), Namby (Ambrose), giving eventually the term 'namby-pamby'.