Ignorance and idleness, I suppose!
I knew a couple who named their daughter
Fiona and pronounced it proudly as FIE-oh-na. It sounded so disapproving, but they had no doubts at all.
And I knew a Leizl once whose name, in her family's opinion, was just another way of spelling
Liesel. I tried calling her LIE-tsl, but she was adamant!