Yes but they obsess over making everything perfectly ssr to the point of both delivering slow and half the time making client side navigations slow as hell after the user is already past the pay walled/marketing material part of your app.

Honestly except for the marketing page and blogs and stuff, most apps are fine without server rendering. In fact I'd say many that avoid server rendering actually feel better simply because next.js makes it really easy to screw up your performance doing it.

Do people really build SPAs that are just websites and not ‘apps’?

That seems to be the only big plus with NextJS and SSR. But a big reason behind that was how Vercel made NextJS accessible to so many newbie devs right during Covid season. I was one of those new learners picking up React through it. Out of all the frameworks, Next was the most well-documented and more straightforward. The extras such as the straightforward routing and the availability of templates by vercel made things all the more easier for many to pick up. Meanwhile React was languishing and most of the other alternatives were just all over the place.

That being said, I'm waiting in the back stage, like many other folks, for tanstack to get production-ready, because of the all the weird crap being pulled by Vercel on NextJS.