This isn't actually how monopolies work. Theoretically, monopolies cannot just charge what they want for a product, unless demand is perfectly inelastic. i.e. At some point, people (consumers) will stop paying or move to a substitute.
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.
I find that this occurs when an infrastructure team considers itself a "platform". The only supplier of an asset that everyone else demands can set the "price" of the asset as high as they want.