Kazumi,
Piaget has been one of the most important Swiss makers of ébauches or movement components for more than 130 years. Their ‘secret’ clients included Audemars Piguet, Breguet, Cartier, Ebel, Longines, Omega, Rolex, Ulysse Nardin, Vacheron & Constantin, Vulcain, Wittnauer and Zenith. More recently (since 1942) they made their own branded watches with PIAGET on the dial. I guess their movements are acceptable.
Originally, finishing of movement (bevels and patterns) had a function. They were to improve performance or to reduce contamination of lubricants or to keep lubricants in the right place for longer. Then, the art of finishing became associated with high-end work and high-end prices. Some brands decorate and polish their movements beyond function to make artistic impression e.g. A.Lange & Soehne, Chopard LUC and Glashuette Original. Even Patek Philippe decorates their more expensive watches beyond functional reasons, unlike their basic watches.
Eventualy, certain rules of finishing and construction became requirements for Geneva Seal. The most important requirement is final finishing and assembly in Geneva. As Piaget finishes their movements at the founding village of La Cote au Fees and also assembles their most complicated watches outside Geneva, they can never apply for a Geneva Seal for those watches.
Although Piaget has a manufacture in Geneva in the same industrial park as Patek Philippe and Vacheron Constatin, so in theory, they could apply for Geneva Seal for watches assembled there, they do not do so because finishing of movements is still done back at the founder's village.
Piaget movement finishing has tended towards good but functional rather than miniature art work. Even so, they never showed the movements in the past.

This old movement 9P2 was hidden in a closed case back watch!
Amazing that nobody could see this except the service watchmaker every 5 years.

This is a modern movement 1208P that will be shown through a clear sapphire case back. Looks pretty good huh?
The difference in decoration and finishing is NOT related to whether the brand wants to show it or not.
Regards,
MTF