Because it's the RANDOM club. "POST WHATEVER YOU LIKE," it can be any topic except for spamming. EVERYTHING talked about here can be put on some other club. But this is a place for (Nearly) all topic. So duh.
Like L Change the World explains, every one of his quirks comes from some deep psychological disturbance; I mean, if you were orphaned at eight and ever since had to emotionally detach yourself from even the most depressing cases, you'd probably be pretty quirky too.
Answer to your question: L is so obsessed with food (mainly sweets) because he has high metabolism.. haha. That's my guess anyway. I know how he feels..I eat all day as well...and I remain exactly the same. I'd hate to think of what would happen if I stopped eating so often.. o_O'
It's only sweets. I firmly believe that he hates healthy food. Bl
And he loves sweets because it's his brain food and the sugar helps him stay up late at night to work on cases.