I think part of the reason is the evolution of common user networking.

Initially, users had low bandwidth connections, and web pages were mostly static with links.

Then came JavaScript interactivity and AJAX.

As users bandwidth grew, we started having heavier frameworks and SPAs.

I believe there is another revolution that is happening now because of decreased latency. Recently with protocols such as HTTP2, web sockets, and edge computing, round trip latency is greatly decreased. This is resulting in UI where more of the logic lives on the server and has led to such libraries as htmx (client) and Turbo.

It will be interesting to see where this settles out.