It is a web platform security restriction that prevents Google Search from coordinating with non-Google caches for prerendering.
Pinterest runs its own AMP cache for prerendering pages linked from Twitter. Bing runs its own AMP cache to prerender pages linked from Bing. Yandex runs its own AMP cache to prerender pages linked from Yandex. They can't use each others' AMP caches and get the same benefits.
Pinterest runs its own AMP cache for prerendering pages linked from Twitter. Bing runs its own AMP cache to prerender pages linked from Bing. Yandex runs its own AMP cache to prerender pages linked from Yandex. They can't use each others' AMP caches and get the same benefits.