It's perfectly possible to show ads without collecting data about your users; printed publications have done it for ages. Currently the big players are very heavily pushing for a model with ridiculous levels of user tracking (to the point that many people believe ads and user tracking are inseparably connected), but that doesn't mean it's the only possible model.

Print publications give their advertisers detailed demographic data collected via surveys and other techniques. The idea they don't collect data about their readers is wrong.

Tracking is needed for relevant ads. No tracking means you still get ads, just not relevant to your interests

So sites need to have their own in-house advertising platform, I guess, because all of the major advertising platforms assume that they'll be able to keep track of how many unique ad views they're getting.