3 ideas
A shokunin is defined not just by technical skill but by an obligation to do the best work possible for the general welfare of the people, independent of pay or recognition. The standard is internal and moral: the work must be done right even where no customer would ever see or check it.
Apprentices swept, sharpened, and prepared stock for years while absorbing technique by observing, and they were expected to 'steal' skill with their eyes. The long, unexplained immersion built judgment and bodily habit that verbal teaching could not transfer.
A tensioned blade does not buckle, so it can be made thinner and harder, producing a narrower kerf, less wasted effort, and finer control. The design choice follows from the physics of how steel behaves under load.