Response 1. Three boxes cost more to make than one. At a total spend of $10k too much in hard dollars is being spent on boxes (and leads between them). At a bigger total spend, boxes and leads are a smaller proportion of the whole.
Response 2. Theoretically exactly the same amp(s) with the same power supply(ies) could be put in one box or in three. The three box version would cost more. But would it sound better? The only difference would be the greater physical separation of the active circuitry and components. How much sound quality can this add?