Making Things Is Fun
Have you ever noticed how there are nearly as many game engines as games? Or how most wiki engines are built for a single site?
It's hard to say "I had fun making this" but insist others should save effort and use your implementation. Your version must be substantially more polished, tested, documented and packaged.
Is it wasted effort?
Not necessarily! One massive advantage of bespoke engines is that they're tailor-made for their first project.
Does your wiki need code highlighting? Spam protection? Support for image embedding? You can build these features with your immediate needs in mind, producing a tool that fits your needs better.