Yeah, I'm pretty sure 9/11 was a contributing factor. Not sure it was the thing, but then again, there probably wasn't just one "thing" that caused all this. It seems like more of a sequence of things, some big, some little, spread out over time, and gradually skewing the zeitgeist to a more negative, pessimistic, unpleasant outlook.
In regards to tech and the Internet in particular, I think the Snowden revelations and the PRISM stuff was a key moment, in terms of changing the perception of the Internet. After broad public awareness of ubiquitous online surveillance became a thing, the Internet lost some of it luster and became more threatening and less welcoming.
More recently, the Cambridge Analytica stuff, along with all the major data breaches over the past few years, probably contributed to that sensation as well.
I can't speak for other countries, but both of these events were like a one-two punch to the gut socially, politically, and economically here in America, and we're still reeling.