I've been looking at some portraits of kings from the 15th century and beyond, and noticed that almost none are wearing crowns. From 15th century England to 16th century France to 17th century Sweden to 18th century Germany, nobody seems to wear crowns, instead preferring hats or wigs and the like. The only exceptions i can find to this are drawings of long-dead medieval kings the artis never saw.
With the crown being the quintessential symbol of power and authority, why isn't it depicted more often?Were crowns really worn so rarely, or was it an artistic choice?
Crowns are a heavy thing, normally a few kilograms. In the case of the Kingdoms in Spain, the coronation ceremony fell out of use in the Late Middle Age, the last coronation recorded being that of Juan I of Castile, and in the case of Aragon it was Juan II.
Rayón, Fernando, "Ceremonias de entronización: Proclamaciones, Coronaciones y Juras". La Aventura de la Historia (189): 69-73.
As for the use of crowns in official portraits, in the case of the Spanish Kings, you may see them accompanied by the crown, but not wearing it, and this presence is only noticeable after Charles II.
Charles II, by Juan Pantoja de la Cruz
Philip V, by Rigaud
Charles III
As for the Crown of Spain, what we have today is just a tumular crown not supposed to be worn, as the lower rim is only 18.5 cm in diameter, way too small to fit any head. The crown was created in the late XVIII century, as the older crowns had disappeared, probably lost in the fire that consumed the Alcázar of Madrid.
F. A. Martín: “Los atributos reales en las colecciones del Patrimonio Nacional, Reales Sitios, nº 97, Madrid, 1988, pp. 42-44