Cause of exactly this reason.
There are always people (read: non-extension writers) who want more. And once they got that, they want even more. If points are done? Shop. If shop is done? Lottery. Lottery done? Paypal integration. Thanks for posts, auto groups, mChat, pages, should I continue.
You clearly do not know anything about developing and maintaining an extension. And you are literally all repeating the same question while it has already been answered multiple times.
We, 3Di and I, do this "on the side". Heck, literally every extension writer on here, does it on the side, besides their main daily job. Even phpBB's Development team. So apart from our regular job and life, we do this, as a hobby. So time is already limited, while code developing is a rather time consuming job.
So, why we are not "extending" the other points sytem? Cause of various reasons, first of all, it's not our extension. I helped develop it but that was long ago and since did not maintain it and it's in dmzx's capable hands. And he's been doing a fine job doing so. Secondly, we have indeed a greater vision in mind, with quite a few of the 'requests' already made (and answered..), so we needed to have a different set up.
One of the biggest issues developing a points extension - or any extension for that matter - is not developing it, or maintaininig it, but satisfying all the new, and new, and new requests. So we created this extension with a different set up, so it is fully extendable. Not only by ourselves, but also by all other extension developers, if they want to. So that will take care of all of the users' "Can it work with X extension?" requests.
And no, points are not useless without a shop extension, it's a matter on how you use them. You can define "costs" to post in forums. Heck, you can even make it so points can be purchased with actual money and you have a paid support forum. That being said, yes, we do have a shop in mind, aswell as some more extension that can extend a points system, but as mentioned before, things take time. And requesting the same thing over and over doesn't change the timeline. We have other things to do, other extensions, our own website, and more. This is just a side project we do to provide an extension and possibilities for the phpBB community.