In the past, companies have tried to optimize and unearth efficiency gains through value chain integration. Reason was that it is easier to communicate and optimize within a company than with external partners. Examples from container logistics include Maersk Line acquiring Damco as part of the P&O Nedlloyd acquisition and Amazon aiming to consolidate the entire value chain from factory to last mile delivery.
In the literature, the explanations focus on lower transaction costs when communicating within an organization compared to the outside and the risk of “hold-ups” is better manageable if you can observe the entire value chain compared to just a small fraction.
Extrapolation: You can argue that these factors and risks are the only reason why we have companies at all, those are basically just a way for humans to work together and communicate efficiently. In a sense, a company is just a collection of specialists who work together on a “platform” called a company.