What's the harm?

Technical risk. Did you read my concerns over inventing Yet Another Templating System?

I've done it myself. I did it because I didn't take the time to understand the existing systems. If I'd continued to use it, I would have had to add more and more features and make the code worse and worse to handle those features.

I don't doubt that eventually I could refine my design into a decent templating system, but I'm not in the business of writing or maintaining templating systems. It's far from what I need to do and very far from what I want to do and it's a huge risk for me to get sucked into such a task.

I don't object to people trying to improve the world, or at least a small piece of it. I do object to people doing their own thing because they don't understand and won't take the time to learn prior art. That's a silly waste of time.