developer gave us the choice of four colour palettes, but refused any other customisations. That seemed like a good compromise to keep the process efficient while still allowing some personalisation. Having said that, some of my neighbours have smashed out cabinetry and fittings to replace them with their own preferred alternatives. It's probably not very efficient to have nearly new materials thrown away and replaced like that.
It is efficient in the sense it is efficient for the developer meaning costs are lower for everyone purchasing in the development. Likewise if a purchaser bails or fails to settle it's not complicated or half finished and costly.