True, but i think the hosting cost is negligible against the time-invested-cost

Is it though? Nowadays you have plenty of good free CMS-es which integrate directly with Netlify. Sure, it might be half a centimeter more complex than WordPress admin but it's still really easy to grasp for many non-tech people (checked).

But even if it was very complex -- which it isn't -- I still fail to see how that supports a model of an ad-supported web hosting.

I think the main cost is producing the content. Researching, creating, and editing the actual words and images.

Sure. Not disagreeing. But those people can make money today as well -- via stuff like Patreon.