What I don’t get is why they can’t go back to contextual ads. Should be obvious to figure out that users following people posting about topic X might actually be interested about commercial offerings in field X.

It really is. Most of what's wrong with social media, and the modern web in general, can be tied back to the perverse incentives that an advertising-based business model creates. If your goal is to drive traffic to view ads, then you do whatever drives traffic, which in the social media and and journalism landscapes is to create outrage and controversy. Advertising as a business model is the problem. We need to fix that. Installing an ad-blocker is a moral choice not to support that business model, and I encourage everyone to do so. The sooner we kill web advertising as a viable business model, the better. They'll find something else.