We should be explicit about what happened:

Google and Facebook skimmed off most of advertising revenue that previously supported journalism.

Then neither originated new news in quantity or quality to replace what they ate. Revenues (from ads) without costs (of paying journalists) = their profits.

Now, we have orders of magnitude less professional journalism.

When you boil it down, their business models are less about being clever and more about redirecting a huge, previously-social-good flow of money through their toll gates and taxing it.