Why did it take so long for christian kingdoms in northem spain to expel non-christian people from the iberian peninsula?

Spain and France do not, in fact, share the Iberian Peninsula. Conventionally (and properly) understood, the Iberian Peninsula is shared by the nations of Spain and Portugal, with several smaller ethnic groups (Basques and Catalans, for example) laying claim to political independence in the same area. Portugal is the other major country on the Iberian Peninsula. Other countries on the Iberian Peninsula include Andorra and small parts of France. (Over 95% of French territory is not on the Iberian Peninsula whereas over 90% of Spanish, Portuguese and Andorran territory is.)