Napoleon made his younger brothers kings across Europe. The Kingdom of Westphalia no longer exists, but Spain and the Netherlands are still monarchies. They've avoided the regnal names of Bonaparte kings -- Joseph and Louis, respectively -- in the interim 2 centuries.
But if a Joseph came to the throne of Spain tomorrow, would he be Jose II? The Spanish were famously unhappy with Joseph Bonaparte's appointment. Would the new monarch just be Jose I, and the first one ignored in numbering like Charles the Fat is in the numbering of French kings? (Likewise for Louis I and II of the Netherlands.)
In the eventuality of a José on the Spanish throne, he would be José II. Although acknowldged as José I, in Spain we tend not to use the regnal number because there has been only one king named José. The same applies for King Amadeo I, whom we we refer to as "Amadeo" or as "Amadeo de Saboya" for the same reason as José. It is not about liking or disliking those kings, but rather that they were exceptions among the Spanish nomenclature. We have had 13 Alfonsos, 7 Fernandos, 6 Felipes, 4 Carlos, and 4 Enriques, considering only the Castilian regnal numbers, but there were a number of Alfonsos and Fernandos in Aragon as well, and a few Carlos in Navarre.
Other instance of not normally using number is Pedro when talking about Castile, as there has been only one Pedro. Former king Juan Carlos is normally referred to as Juan Carlos, without the according number. Think of the Universidad Rey Juan Carlos, in Madrid, or the many places with an Avenida Rey Juan Carlos, more frequent than Avenida Juan Carlos I.