I don't think we're even that much more pessimistic, overall, though we might be.

24 hour news cycle may do something, but we had daily bad headlines for a long time before that.

If anything new is making us depressed, it's likely algorithmic attempts on our attention. A/B testing on the most engaging content, leading to addiction, as in people who hate that they waste all their time on their devices and yet can't bring themselves to stop. At least some of that may lead to negative affect, including pessimism but also dysmorphia and rage etc. depending on what the A/B testing finds works best for your demographic.