You are not locked in by a single supplier who refuses to tell you how to interface to a competitors product. In a serious production environment every component is dual-sourced. They have several suppliers or potential suppliers. If one demands too much money, they change. It may appear possible to have a single supplier and a tightly worded contract.
Companies go bankrupt however.
If a contract argument goes to court you may well be out of business before you supply of parts is resumed. Similarly, in a production environment, downtime is unacceptable. Companies need guaranteed, strong, support. If the vendors recommend a maintenance engineer who is incompetent you have to be able to go elsewhere. If you buy a car and the local garage is useless, you take it elsewhere for repairs.