So why can't the same be done on websites? If numbers of views can't be confirmed without spying on users or trusting shady actors to do that for you, it means the business model that is based on this metric is skewed.

If one network offers approximate numbers from an expensive external audit and another network offers "exact" tracking through cookies etc., which network do you think advertisers will spend with?

Exactly such egoistic and short term thinking led us to the current situation and the widespread usage of ad-blockers, no?

In general, newspapers serve the same ads to all their users, so approximate circulation roughly correlates to an ad's reach. Websites don't, so even if you knew a website's pageview count you would have no idea what percentage of those pageviews an ad appeared on.

And that, eventually, is going to have to be good enough for online publishers and advertisers.