Because those are almost non-existent. There are many web-apps that need a fair bit of interactivity but a full SPA is overkill. I'm thinking things like JIRA where the interactivity of the kanban board is good but most of the time I'll just middle click to open a task in a new tab anyway, being a full SPA is a net negative. Most of the rest deserve to be a real desktop and/or mobile app.

SPA's aside web dev hasn't changed much in a decade, it's just been framework churn.

I've spent most of the last decade working on data-intensive web applications which definitely deserve to be SPAs. There's lots of opportunity, especially if you're willing to move away from the "retail" public-facing web.

What do you mean by data intensive? I'm thinking something that looks like a bloomberg terminal, complex tabular data or complex visualizations. Those are cases that should never be a web app at all, even with recent improvements HTML is a document format and horribly suited to those use cases.