You've moved goal-posts ;)
Sorry, but there are no donation based major national news organizations or donation based search titans with historically large market caps or donation based social media empire whose CEOs political whims shake national elections the world round. Facebook, Google, PictureHostOfTheMoment, and the media giants with traditional business models are the essence of what most people are using their time on online. That's "the web" for most people most of the time.
I mean... Grab a random high-schoolers phone and see what percentage of services they're using are (in)directly funded by advertising and advertisers.
Your observations about the economics of the bulk of web-development are probably correct, but relatively minor compared to the mega-billions in suboptimal efficiency in every other aspect of those organizations... And the issue is always that "sustainability" is not growth, and growing frequently requires actions that are unsustainable in the long-term to achieve. Businesses grow, transition, and reshape themselves within the context of new revenue streams, and acquiring those new revenue streams is how you make owners richer and secure any desired financing.
So yeah, really, as of todays date "the web", a la "TV", is a pure advertising apparatus to capture audience and move product with peripheral benefits in political manipulation. Other models have not been validated by the market, nor consumers. Remember we all want ads, in the abstract.