Look under: "unlocking value". There are pros and cons of being big. One of the cons (at least perceived) is that a big company tries to have "synergistic" sales sometimes at the expense of what is good for the product group. Example: the MS SQL server group might be able to make more money if they supported other OSs but the parent won't allow it. The cumulative amount of sales might be better since a lot of people stick with Windows because they want Office and use Office because they have Windows. For Blackberry as far as I can tell their big selling point back in the day would have been to spin off BBM and a security appliance that would support all vendors equipment. Anyways the games the transition teams/banks can play is trading the estimated synergistic sales against the hypothetical unrealized sales forgone because of corporate pressure.
Add to that the dillution of power/responsibility for success when you are just a 10M business unit in a 30B company, versus the whole pie, the reduction in innovation as financial and project controls get more formalized rather than just being a skunks works company trying to see if they can make their 100k market into a 100B one.