Several times a day, people make clearly off-topic posts on MSE. And I've noticed something of a trend with these posts.
Obviously, people vote-to-close them as off-topic. But they also get downvoted heavily. The thing I noticed is that... they don't usually get deleted. Or at least, not nearly as quickly as they get closed. A question closed in minutes will often linger on for hours or even half-a-day before finally getting the 3rd delete vote.
Yes, far more people have close-voting powers than deletion powers. But I think there is an additional reason for this disparity: people with delete powers don't see those questions.
When a question is sufficiently downvoted, it no longer appears on the front page. That is good, in that it removes bad things from the front page. But, that also means that the only way to find that question is to look at the Questions page. And that page is simply not as frequently visited as the main page.
As such, I think we would deal with these questions more effectively and efficiently if they weren't downvoted. Yes, they're bad, but that means they need to be gotten rid of. And getting rid of them requires visibility, which downvoting inhibits.
It's an odd catch-22.