Who is paying forty master builders? Some billionaire probably.
https://de.m.wikipedia.org/wiki/Michel_Guyot
The son of a small business owner developed a passion for history, historic preservation, and horses from a young age. Trained in the military as a competition rider, he opened a riding stable at the Château de Valençay in the Indre department in 1972. In 1975, Guyot and his brother Jacques, who was four years younger, purchased the Château de La Roche in the Sologne region, and in 1979, they acquired the dilapidated Château de Saint-Fargeau in the Yonne department for a minimal amount. After failing with a "high culture" festival, Guyot succeeded in financing the castle's restoration through large historical spectacles involving the local population. The castle grounds also house a collection of old steam locomotives.
In the mid-1990s, he conceived the Guédelon project: since 1997, about 60 employees and 200-300 annual volunteers have been building a small fortress in 13th-century style, located 40 kilometers southwest of Auxerre - using exclusively medieval techniques. The planned construction time is 25 years. This project has also become financially self-sustaining.
Of course a real castle would probably have been made of wood which is both easier to remodel and also needs it anyway as wood burns and rots over time. (in turn meaning most castles have left no evidence they ever existed other than what is in the local records) What we see is the small minority built of stone.