
Large established manufactuers have a basic structural design that has been developed and refined over several decades.
Minor changes are made to this structure, which is primarily the chassis (e.g. BMW CLAR, VW MQB. Merecdes MFA).
Since production happens at very large scale in assembly-line factories, a single design is made for each usage class, and the design is done in-house, over several years, linked to a production process.