I've seen multiple corporate re-orgs (Fortune 100) and you are right -- internal monopolies cannot just charge what they want. Eventually, internal customers get fed up and "revlot" -- then you have a corporate re-org where IT infra/services get distributed across business lines or lower.

Eventually that blows up too -- re-composing data at the parent level (e.g., for quarterly financial reporting) becomes too exhausting and the company decides to revert to centralized services.