> But that does not explain why people send their text based pages as javascript.

Probably because they're using front-end javascript frameworks which do that, and because they were taught that this is the best and most efficient way to render anything on the web. No one wants to make a special case for text because it seems inelegant.

But it's not the best and most efficient way to render everything. If you have a mostly static site, you don't need the front-end framework.