This is a gross oversimplification but the purpose and goals of their expeditions were just completely different. Even the earliest Spanish expeditions were (in part) state-approved, armed and essentially get-rich-quick plundering schemes. The existence of advanced (but less well armed) urban civilizations just encouraged them since it meant potential for gold.

A lot of now-famous early British colonizers were basically groups of funky religious malcontents hoping to establish their own little theocracies. Their state approval was more along the lines of 'good riddance'.