IMO there's like 4 places troon names come from
1. Just do the girl version of their real name.
2. The name of the girl that got away when they were young.
3. Some character or celebrity they're fixated on.
4. Something they think sounds demeaning due to either being childish and cute or just downright sexual.
Natalie is super common because it hits like all of them. Its a substitute name for Nathan, it was a common name when most of them were young, references Natalie portman (and other porn people), and it sounds rather feminine - ends with -Ie all that,