Sorry, I have to disagree with this. I was a jury member for Russian competition, the majority of the jury were the community members (we are special because we are based on Wiivoyage, not on Wikipedia as everyone else, but this is not relevant), and we spent quite some time deliberating how to select the final ten winners. It was not easy, and not everybody agreed with everything, we had to go through several rounds of voting and discussions, but in the end I feel we have done a good job (though I am sure a lot of people are not going to like what we selected, we already got some criticism from the community). And I did not check the numbers but I think we have stable high participation which is either growing or oscillating year to year, but definitely not steadily declining (but at some point probably we will have all the monuments photographed, and it would starts going down, which is natural).
Best