It would have been inconceivable back then (mid noughties) that the whole thing could be done client side. The Web has come on a long way.
These days I tend to hate WordPress with a passion. Occasionally I will be asked to peek at some technical problem with a WordPress installation and it's never not like opening some awful Pandora's box of out of date, brittle, scary plugins, these days most of which seem to be trying to upsell via ads in the admin.
However I will always be thankful for WordPress and what it enabled in its heyday, and say a silent prayer of thanks every time I think of the people tasked with keeping creaking old sites alive.