The reason has to do with how the wind was blowing in a particular part of the world in August of 1588. It's that specific.
Want to know the reason much of North America speaks English and not Spanish? It all boils down to a single day in the English Channel in August of 1588, says Yale University history professor John Lewis Gaddis. The Spanish Armada was cleverly chased out of British waters by a rag-tag British fleet that set old ships on fire and pointed them right at the anchored Spanish fleet, causing the Spaniards to cut anchor and flee. Because of the way the wind was blowing, the Spanish ships had to sail all the way around the British Isles (about 2,000 nautical miles) to get home and were soundly defeated. That led, John posits, to the rise of the British empire. John's latest book is the fascinating On Grand Strategy.