Ever heard of the innovator’s dilemma? Don’t underestimate the inertia of large companies and their unwillingness to pivot from their cash cow.
Demis will get an offer he can’t refuse - they’ll make him the CEO of Alphabet and have the whole company go all in - the question is when.
If the new cow doesn’t have cash, it is better to stick to the cow you know.
Google specifically has a track record. You could have made the same argument about social media (Google+) a decade ago.