One reason that I can think of is that a spam account here doesn't tend to get very far. Sure--they could spam the New Submissions list, but they'd have trouble

One reason that I can think of is that a spam account here doesn't tend to get very far. Sure--they could spam the New Submissions list, but they'd have trouble getting upvoted and thus polluting the front page. They could create a bunch of accounts that all upvote an article, but it's easy to detect articles that only get upvoted by low-reputation accounts as clear spam. I guess the bottom line is that the reputation scores here provide a lot of high-quality signals for spam detection that a normal site wouldn't have.