Engineers will do what is possible with the time and budget they're allotted and with the capabilities of the development team. If business management decides a product has to be out the door in a year, and research is happening simultaneously with development, and the team is fresh, there isn't much chance the product will be optimized for performance.
Noise impacts the quality of sound more than the vast majority of listeners understand. In most products, the spatial cues are buried in the noise. This is one of the reasons by the way why some amps or receivers sound different than others even at the same SPL.
There are so many factors related to achieving a low noise floor besides the numerous design decisions that have to be made within the power supply design. Design departments that understand this have a noise mitigation protocol that is audited throughout the product development process.
