To me the biggest contributor to my lessening activity is the massive loss of custom builder/modder activity over the past few years. That was how CPF got started, and those innovators were the lifeblood of the forum for nearly two decades. They presented their ideas here, we bought and beta tested their gear, we helped them improve and refine them, communicated with them, became friends with them and with other members who also appreciated their work. There were thriving conversations in the Cool Fall, McGizmo, Dark Sucks, Okluma, Mac, Photonfanatic, MBI, Muyshondt, forums and threads, among many others. But almost all of them have disappeared, many to other forms of social media like facebook and instagram. I understand wanting a bigger customer base for selling lights and that is fine. But their original friends and fans, the ones who took a chance on their lights and helped to develop their craft are here. Or, were here. They wouldn't be where they are without CPF, and it is disappointing that they no longer see fit to visit or post here about what they are up to. To me this is a massive blow to the community. These are the lights and mods that many of us were interested in, and the friendships that we developed around discussing them were great. We talked mods, LEGOs, upgrades, usages for specialized lights, everything. There isn't a whole lot to be said about most of the boring soulless production lights out there other than how bright they are, so they don't foster much interesting discussion.
This is likely close to the answer…I don't look upon the changing nature of the forum as a decline, but rather as maturation. For example, a quick search of the forum topics on a given subject will often show that a question has been addressed and well answered in one or more existing threads, eliminating the need for a "new" thread. Arguably this makes it seem like there is less activity now compared to previous years, even though the information is still there. Related to this is the generally increasing level of knowledge and experience in the community that this forum has helped foster. I interpret this as operating to reduce the number of "entry level" threads and posts that are submitted. Finally, the pace of innovation in emitter development today as compared to ten years ago seems to me to have also matured, so that we're now getting better refinements of already good products, as opposed to new and ground-breaking product announcements. Refinements of existing products are not as exciting as new and innovative developments.
As for me., I've acquired more lights than I can ever use in my lifetime (SHTF scenarios included). I'm no longer excited about a 5% incremental increase in lumen output for a light I already own, despite the best efforts of the marketing department to induce me to buy the new and improved version. However I'm happy to buy a new light that fits my needs and preferences if it offers a meaningful improvement over an existing product that I use and rely upon: a quick look at a light's specifications will often tell me what I need to know, and that is a function of experience, combined with the general "enlightenment" I've received from participating in this forum over the past ten years.
Don't get me wrong, there are quite a few higher-end lights that I would love to own. I'm uncomfortable however in dropping $500 - $600 - $700 or more on one or more of my "if I win the lottery" lights, mostly because I have more pressing uses for my money.
The bottom line? The forum hasn't declined, it's just that we've collectively matured. And the information is still here for the asking. it just takes more to excite us now. (My two cents.)