Not Anymore なくなる

なくなる describes a gradual fade, not a sudden choice, closer to “I’ve stopped doing this somewhere along the way” than “I decided to quit.” ことにする, by contrast, always names a deliberate decision, a useful pair to keep distinct.

These sentences chain two なる clauses together, one positive change causing a negative one, 明るくなって(became bright)、怖くなくなりました(stopped being scary), a common way to describe cause and effect unfolding over time.