I think you'll find its the SIAM bit which is not policy rather than "Towers" as such i.e. hiring one of the SIs to take responsibility for all the other outsourcers. In-sourcing that integration role makes much more sense, although it will take time and money to find the right people and build a properly responsible team with the right culture and capabilities in each department. It still makes some kind of sense to outsource the mobile phone service to a mobile phone company, the cloud provision to a cloud provider etc