One of the things I've seen cripple large organizations is waiting for the common infrastructure / services becoming mature enough to be used in production.
Teams are kept in a holding pattern, sometimes for years, while waiting for the teams to deliver their common infrastructure / services solutions, and they're actively discouraged from building their own solutions, because the enterprise-wide solution is "just around the corner".
It depends, but generally yes. Collapsing to 1 may or may not be a good thing, but you probably want less than 3-5 different DBMS, CMS, Cloud providers, printing services, source control systems, office supply/equipment, etc.
At some level, absolutely. Your organizations aren't usually totally independent units - they need to interoperate with other organizations.
To the extent that the spaghetti of infrastructure prevents effective interop, that's a problem.
And as the need for interop grows between two orgs the cost of the various hacks, shims, and other cheap adaptations, escalates, until unification of infrastructure starts looking awwwwfully tempting.
Of course, unification comes with its own set of problems.
