IIUC the intent behind AMP is that the AMP page is the destination.

Except when it doesn't work.

I mean, I dislike broken AMP pages as much as any other user. But from the perspective of Google management, a broken AMP page is a bug report that you file with the relevant engineering team. An interstitial or aggregation page that some third-party puts up is outside of your control, and so you disincentivize it with product incentives.