Camera and lens sales have declined, declined quite a bit. There have been many stated reasons for this decline, starting with smart phone cameras taking the place of small P&S cameras. That is a good reason for the decline of many entry-level cameras; but higher quality DSLRs have also been on the decline. I think that has been partially caused by the decline in photographer businesses and careers due to decline in magazines and newspapers. They have been going out of business and the few remaining no longer are willing to pay for photographers on staff and are also finding that smart phone videos are good enough. But there are other causes.
One subtle cause has been the aging of our population. The older photographers are finding that they now can no longer handle the large and heavy “pro” DSLRs. These changes in the high-end of the industry have occurred at the same time that the younger generation has grown up with small digital devices, which now have cameras in them. The result is that the demand for “cameras” is less and has been squeezed from both ends.
Another cause is the change in interests of hobbyists. How many of you remember hobbies like Macramé, stamp collecting, cooking, printing pictures, etc. If you remember them you are getting old. The younger generations have different hobbies like keeping their thumbs and eyes busy with their smart phones and small computers while they play games, cruise the web, take selfies, etc. If you think differently, go where there are younger people and look around .
Photography will not die but it will change. Down the line a ways there will be less art hung on walls, fewer wedding photography books, etc. In addition all documentary photography will be videos and the camera as we know it will be gone. There will be no more line-ups of photographers with enormous long zoom lenses along the sidelines of football games, etc. The coverage will be with smaller video cameras. Still images will diminish accordingly as current living generation’s age and die.