> SPA is not only about seamless transitions but also being able to encapsulate a lot of user journey on the client side, without the need of bothering server too much.

True, but as a user, I don't want you encapsulating my journey. You can wax poetic about hypothetical book categories, but the reality of SPAs is that they break back buttons, have terrible accessibility anti-patterns, attempt to control my attention, and expose my computer to all your bad security practices. SPAs usually contain half-assed implementations of half the features that ship standard in a modern browser, and the only motivation for all that effort is to make the site more favorable to the server's owner.

When a site is implemented with simple HTML and careful CSS, I can configure it to my needs in the browser quite easily. That's a site that favors me, not your opaque blob nonsense.

Why is this being downvoted.

I agree, as user make it fast and don’t break the web. I see so many SPAs with bad usability, like back button not working.

A shopping site doesn’t need to be SPA.

A drawing app, 3D modeller, collaborative whiteboard, video chat, those type of apps fit the SPA model.