Site traffic is indeed down in recent years. The largest decline was when Facebook introduced "boosting," and stopped showing our posts to 90%+ of our Facebook followers overnight. I despise advertising, so I was unwilling to cave to their demand to "boost" our posts into ads. I'd have been happy to pay a reasonable monthly fee to reach our audience there, but that option was never available.
That big dip in traffic came with a big dip in donations, and as a consequence I eventually had to move from a part-time day job to full-time. The sharp reduction in free my time led to a sharp reduction in original content on Damn Interesting, which further shrunk the pool of people willing to donate.
This is a spiral that some would classify as "death," if I were willing to let it die. But it settled into an equilibrium where it pays for itself, makes a modest profit, and remains rewarding. Frankly I'd probably still do it even if donations dried up entirely, the research and writing give me a sense of purpose that would be difficult to replace.
I used to hope that a wealthy benefactor would discover us, and decide to fully fund our project for a few years, giving us space to realize more of the project's potential. But such offers come with strings attached, and I don't have the stomach for most of those. Perhaps I am broken.