Many nations started colonisation in the 15-19th centuries after Castile found the Americas so why, when the Norse explored Greenland and Vinland, didn't more western nations look to colonisation at the time?
Because they didn't know the Norse discovered anything. No one knew until the modern times, when scientists started reading Viking sagas and realized Vinland could be the Americas, but they weren't sure until archeological digs in Newfoundland confirmed their suspicions.