Free, competent, altruistically interested
Pick two when looking for leaders.
The "volunteer leader problem" boils down to looking for an altruistic individual who's capable and willing to put up with a ton of shit for... love of X.
There aren't many. There shouldn't be any, but some people are awesome.
In reality, you end up having to substitute some package of incentives (prestige, authority, etc.) in order to entice on-the-fence candidates, and then ride herd on ensuring they don't succumb to their baser instincts.
So when mods say mod tools are important, what they're really saying is: "I put up with a lot of shit, to make you money, and I don't get paid. Give me something in return that makes me feel like you're thankful."
Reddit's been pretty bad, historically and presently, at doing that.