A crown carved as a free-standing object has a problem no applied ornament has: it is pierced all the way through, and it sits at the highest point of the chair where every knock arrives.
The arches of a crown converge at the top and spring from a band at the bottom, and each arch is a slender curved member with grain running out at both ends. Carve the whole crown from one block and those arches are short grain at their most vulnerable point.
So the crown here is built rather than carved from solid: the band is one piece with the grain running round it, and each arch is a separate piece with its grain following its own curve, let into the band at the bottom and joined at the finial on top. The joints are then covered by the carved detail at both ends - which is exactly where a real crown carries its jewels and mounts, so the ornament has somewhere honest to be.
It means the crown survives being carried, dusted and knocked, which a single-block crown will not do for long.