I think there are a lot of reasons. Here are a few of the bigger factors, imho:
1) When I was a kid, I got tonsillitis every winter. My mom would always try to wait it out, but most years I’d eventually end up taking antibiotics. This probably happened every year from about age 5 or 6 until about 13. I stopped eating meat when I was 13, and I think that was the first year I didn’t get really sick during the winter.
2) I have a gluten allergy that I don’t think is related to leaky gut, and it took me until I was in my early 20s to figure it out (I can trace the symptoms back to at least age 11). Assaulting my immune system with years of gluten likely did not do me any favors. I quit eating gluten completely almost three years ago. Some of my (then-unrecognized) candida symptoms diminished for a while.
3) I drank way way way too goddamn much last year, while living mostly on free fruit and free gluten-free baked goods and (not free) Thai food and stress, and I worked out really hard. I think I’d had a slight-to-moderate candida overgrowth for a while, and last year’s poor decisions sent me spiraling into a booze-and-sugar-fueled pit of candida doom.
I was a gluten-free vegan who ate homemade cultured veggies a lot and didn’t eat many processed foods compared to most people and drank a lot but not as much as many people I’ve known, and I still ended up sick :p So it goes? It’s better that it caught up to me now, honestly. I’ve been forced to make changes that are allowing me to heal now while I’m still young (while it’s still easier) and to prevent years of even worse damage.