Nice reading comprehension.
It's not the 30 seconds that matter to me, like I said it's the cumulative total of wasted time. If someone (and I should add that it doesn't even need to be the same person) drags on races for an extra 20 seconds because they entered a race with no intention of racing for a dozen races, I miss out on a couple of races I could have done if nobody was holding me up AFKing. In an evening I'd lose out on quite a few races if AFKers were that prevalent. Missing out on a dozen races because someone is purposefully entering an AFKing would annoy me, waiting for an AFKer once wouldn't, though I certainly think it should be discouraged (some AFKs are unavoidable though).
I'm not one to get too annoyed at such a thing, but if someone was faced with AFKers that often during an evening, I can see how they'd get annoyed, even if the person they eventually get annoyed at only did it the once. If I saw the exact same person holding everyone up over an evening of racing I might say something, but I'm doubtful that happens.
