Spain entered into second tier status after the Battle of Rocroi (1643) and the Franco-Spainish War (1635-1659). By that time, it had suffered too many losses to take on the British colonies. Its economy had been eroded by inflation, huge debts from its many wars, its years of grandeur had made them arrogant and non-innovative, and its economy could not compete. Spain had been fighting the Dutch Revolt since 1588, then the French in the Thirty Years War. There are only so many wars a country can handle.
So in the years when the English colonies were most vulnerable (1607 to 1674), it was already pre-occupied with far greater concerns. Afterwards, the dominant threat was France, and it would not make sense for Spain to alienate England (and England might get the better of them anyways). And before this time (pre-1588), there was not enough wealth on the Eastern Seaboard to encourage Spain to settle it. Spain already had too many land claims to settle as it was, and such marginal territories were going to go to someone else. Mexico and Peru were the major sources of wealth in the New World, as well as Spanish rule in the Netherlands. Its going to devote its resources to them.