Why would a monarch from one country be interested in hiring an explorer from a foreign country?

An example would be King Ferdinand of Spain having Columbus do his exploring for him. It is two fold, in that the riches or the conquering acquires land or resources and it is a show of power, more wealth equals more power. The explorer being from a foreign country is another feather in the cap, showing that they have an edge over that country and that the countryman was willing to go elsewhere and work for a competitor.