Can't argue with that, because most public-facing "apps" are mostly read-only. However after a bunch of years working for a software house I can tell you that there are a lot of "non-user" reasons for choosing SPAs. The ecosystem of all SPAs offers unparalleled developer experience that allows you to create many complex apps really fast and reuse a shitload of components, interactions, animations and whatnot. With basically 0 effort you can also create mobile and desktop apps from the same code. And the talent pool for something like React is a lot bigger and a lot more "UI/UX-friendly" than in whatever "backend-tech" of your choice. I work in .NET and when we recruit devs a lot if not most of them straight up hate frontend or don't care about UI/UX at all so we kind of can't do shit with them alone anyway. It's easier and cheaper to recruit a bunch of React devs.

TL;DR: money math works in SPA's favor, users be damned