The ad-based internet has conditioned people to expect free content, and the internet ad model incentivizes click-bait low quality content because it's easy to publish and provides a place to hang ads from.
Did the demographic that was willing to think hard & long enough to enjoy the old SciAm gradually die off? Or did they just replace eating paid-for healthy brain food with eating free junk food.
(FWIW - I pretty much dropped all the "premium" subscriptions I once had - all dead-tree editions - between ~2000 and ~2010, as either their quality went to crap, or they ceased publication.)
That demographic were always a minority of the general population and I think they still exist. Maybe at one point Scientific American had some pride and catered to this niche because they thought it was socially constructive or something, but clearly they're now gearing towards a more... mass audience.. to get more money of course.
I don't know how else you'd explain an image of the wrong ocean. If they couldn't get the right image, why include an image at all? Of course pictures are appealing for mass audiences, a substantial fraction of whom are barely literate and need pretty pictures (even if irrelevant) to encourage them along.