I think the main thing is that the downsides of SPA frameworks are significantly mitigated in a dashboard app.

Typically dashboards will be accessed on a desktop in an office setting with good internet, so initial load and asset size isn't a huge issue. Then you get benefits like client side routing which feels snappy, and live updating widgets is pretty simple. Of course it's a matter of opinion though.

I doubt that "client side routing" makes a site more snappy.

I think what you mean is that elements shared across pages (the header, the navigation bar etc) do not have to be sent again.

But those are very small anyhow. And you could bring the size down to zero by making them web components. Web components are cached along with the JS that defines them.

Ah yes, thank you for the thorough corrections, you knew much more about this topic than me and correctly guessed exactly what I meant.