I don't see how SPAs and mobile apps necessarily conflict with the ideas behind the semantic web.

Anyway this claim seems to reverse cause and effect. SPAs started getting hyped a lot after it became apparent that big tech institutions weren't really going to pursue semantic web.

There's no real meaning in the claim that "Zelenials" did semantic web in. As far as I know, Zelenials never took a vote and decided not to pursue semantic web. The relevant agents here are huge institutions with the power and desire to shape developments in web technology. Google and whoever.