I see a thread every now and then about upgrading cameras. And then there are the threads about the decrease of compact camera sales (etcetera, you get the idea). In many of these threads it's stated that most people have been upgrading regularly, but are slowing down now because the cameras are good enough. I do not believe that is the came universally.
I think that only 10-20% (number not based on any single hard fact) of photographers (here meaning anyone who owns/uses a camera) have actually bought a new camera before their old one stopped working. And I actually mean 10-20% of photographers in the entire history of photography.
Older forum members sometimes remember how they had an SLR for decades before buying a new one. Guess what? This applies now as well. I have recently been at a graduation ceremony, Not a single camera of about 40 (not counting phones) was newer than 1 year. That includes the paid photographers' gear. I've seen compacts that must be about 10 years old now. And people still use them, and will continue to do so until the cameras die. They most certainly don't feel the need to upgrade (before I got into photography, our family's grand total of cameras was 1 film SLR (has been working for 30 years and still does) and 1 digital (6 years, then it developed glitches and finally stopped working 2 years later), and then we bought a DSLR and it only went downhill from there ) So from an everyman's point of view, upgrading is an unnecessary expense.
That leaves the enthusiasts, semi-pros and professionals (They need the latest and greatest to keep up, right?). But in reality, many pros stick to what an enthusiast would call 'ancient', or at least 'outdated'. At events here, the newest pro cameras that are actually used by pros seem to be the D3 and 1D Mk. III-IV series, and many have even earlier flagship or semi-pro cameras (we need to distinguish between self-equipped pros and the ones that are spondored). I believe this is because the cost of upgrading is so high, so they really want to get the most out of their 6-8k cameras. Most only seem to upgrade when their cameras irreversibly disintegrate in some way.
So that's where the hobbyist/enthusiast crowd come in (myself included ). WE are the group that accounts for most of the inhabitants of this forum and others. WE have stopped upgrading every other year, not the entire world. We just happen to be, well, more enthusiastic and vocal than the other photo demographics.