I think some of the advantage comes from synergies of having microarchitecture development and process development under one roof. You can fine tune them togeth

I think some of the advantage comes from synergies of having microarchitecture development and process development under one roof. You can fine tune them together to get the best performance/power ratio. Even if both alone are just on par with the competition, together they are still ahead by a few iterations. Also they get out new products a bit faster. The problem is that by switching to another fab they lose these advantages.