I presume they thought it was a cute name, they seem to like the fashion for cutsie names.
And I presume they thought it would look like a loving tribute to the queen.
But to many people it looks like a thoughtless crass move of using something deeply personal to an old lady, who your relationship is strained with, and where the only people ever close enough to use the pet childhodd name have all died.
The fact so many peopl winced and thought how crass and unkind, I'm sure wasn't their intention. I'm sure they thought eveyone whould think, how sweet and how especially close to the Queen they must be.
It's just another example of their extraordinary inability to understand how they come across or how their behaviour will be interpreted.
It's quite staggering how they just get everything so wrong.