Why is my prized wiki withering away?

I hardly get any contributors, and of the ones I do, about 66% are vandals.

I've built a defensive wall to block off vandals. Shame is, vandals are creating new pages (that include words like penis) and the "defensive wall" is blocking off harmless people.

There's one thing for it, I guess.

Install some sort of filter on my wiki that takes out unkind words, but how?

My wiki is

And a list of blocked vandals: