It came from a period around my early 20s when I was into furry as a concept but didn't have a fursona, I would often say "rawr" as a playful thing & a friend started calling me "lion" based on that, I vibed with it & that led to me adopting it as my sona species and from there I became a Lion Appreciator in general. it doesn't go way back into my childhood or anything but it just felt right. i've always loved cats and lions are very large cats with cool hair and what's not to like about that?