Why are large companies so difficult to rescue (regarding internal technology)

As part of this new focus on unification, SuperRentalCorp would like to create a single unified API, so the outside world thinks the company has an internally unified tech architecture. SuperRentalCorp has 20 major databases, run by 20 different teams, in at least 10 different countries, many with a history of operating as an independent company, each team guarding their data, partly out of security fears, partly out of concerns about local laws regarding user privacy and the regulation of international transfers of user data, and partly out of sheer stubbornness. However, SuperRentalCorp has retail outlets with POS (point of sale) systems which talk directly to specific databases, and the path of that write (straight from the POS to the database) is hardcoded in ways that will be difficult to change, so it will be a few years before the company can have a single write-point.

Source: www.smashcompany.com