This standardisation of design and equipment means that companies can share the costs of making an interior among the entire range. This means that customers can benefit from having a lot of high-end equipment and premium designs while spending less on a car. This is especially true in the case of infotainment systems. Different companies share the same infotainment systems (Kia, Hyundai; Jaguar-Land Rover, etc.). This broadens the number of models that use that particular infotainment system and hence it results in lower costs. This also leads to more refined and well thought out designs.
Plus, this standardisation helps people choose what they want based on dimensions, and not features, to some extent. The idea of a design language gets emphasised more because of the standard interiors, as we spend more time in the interiors of a car. It doesn’t matter which interior you see, you know what brand it’s from immediately because of the design.