According to a couple of books about the Armada which I have read lately, there were several reasons for its failure to achieve its mission.

One of the primary ones was that Parma, who commanded the land forces which were supposed to be embarked to invade England, made no preparation to do so or response to Philip's and Medina Sidona's communications telling him to prepare to operate in conjunction with the great armada.

The battle(s) between the fleets were relatively minor engagements even though both sides pretty much used up all of their on board ammunition.

The Spanish ships were so unweatherly that, once they anchored they would have been unable to return to England against any sort of resistance, which was why they attempted to return to Spain by the Northern route around the Isles. They could not go anywhere near the wind.

Although this was the most famous armada, Spain sent several more up to 1596.

These armadas were so expensive that they contributed materially to Spain becoming a lesser power, as they essentially bankrupted the treasury.