Why are parents so opposed to giving wiggle room?

Why are some parents so firm about the names they give their children? I'm having a hard time articulating exactly what I mean, but basically, it seems to me that parents are frequently willing to die on the hill of giving baby a name that they won't be able to tailor to themselves when they get older, and/or not allowing them to tailor the name.

For example, both my maternal grandmother and my father have names that really don't have nickname options, AND neither of them have middle names. They have both bemoaned this all their lives. My husband, conversely, has gone by his middle name his entire life and is grateful for it because to quote him "my first name just feels too old and too tied to family history." When we named our son, we gave him a very unique first name, but two usual middle names in honor of grandparents (this wasn't about choice ironically, it was about matching the fact that I also have 4 initials). When he's older, he's got so many nickname options or can just go by a middle name like his dad does.

This post was inspired by a woman I met fairly recently whose name is Katherine. She introduced herself as Kate and I said it would be easy to remember because my best friend's middle name is Katherine and she also gets called Kate by her closest loved ones. Kate replied, "Oh I love that! I don't have a middle name, and growing up, my parents wouldn't let me shorten my name." I was shocked! I asked her why and she said they told her when she was younger "We named you Katherine, not Kate, not Katie, not Kathy. Katherine." She said she always hated it and now only answers to Katherine at the doctor's office.