Because that's not what I was paid for. If you'd like to front the money, I could build those things too. Although I'll admit right here that those things you ask for are not my specialty so they may not be built to the highest standards. Web Applications though, is what I've spent my entire career on. So while you ask why I don't write those things, you might as well ask an Electrician why he didn't build his own electrical grid for your house to be on while he was wiring up your house. Do you understand the gravity of your question now?

Trolling aside, if you're more concerned about the why. Then I'll leave you with this. When this forum is done, it will be bitcoin that built this forum. That's point 1. Point 2 and probably more of interest to theymos, the forum software that is already out there did not meet the requirements that theymos wanted. The key reason being that he wanted more control over what could be done to the internals of the forum. This approach allows him to build specific tools that are not found in other forums tailored to the needs of this community. Some of these tools are more comprehensive moderation tools, more expansive reporting tools, and more precise banning tools to deal with spammers and scammers.

To be fair, he did have a number of these tools that he wrote himself. We've just rolled them into the new forum so they act and feel as if they are a part of the software and not just an after thought or mod.

You also missed one more thing. The fact that we're building this from the ground up means that the community can have an active hand in the building of this project. I've already listened to those that are helpful and integrated some of their ideas into the forum. Things that the current version of this forum does not support (spoiler tags for one, highlighting admin/mods for another).

With that said, it's all been paid for already. Why not help make the forum better than all the rest by giving it a try when the next beta comes back up and giving some constructive feedback?

Also, the reason why there are so many "other" forum software is because there is more than one way to use a forum, and often times more than one use case that determines how that particular software is going to be built. This is a use case for the bitcoin community. To go back to the house analogy, it's like having a say in the blueprint as you are building your house. Do you want higher ceilings? A marble staircase? French doors? You can make those suggestions and if they are within reason, we can just build it.