When my parents got my my first ring ever growing up, I wore it on my ring finger. Because it was my 'Ring' finger. At the time it made the most sense to me. I still say it was a logical argument.
And I wore a ring on my ring finger up through high school and the first year of uni. Wasn't a promise ring, or a purity ring, just a ring I wore. I was used to it, and wearing rings on my right hand always bothered me in regards to my writing with pen or pencil.
But in university I got sick of people asking me if I was engaged, or if it was a purity ring, and then explaining why I wore a ring on my ring finger when it was neither of those things. So I stopped wearing a ring on my ring finger.