Quick question: I'm playing my first game on nprmal difficulty, after a loooooonnng period of learning, and I'm playing as Castille (now Spain)
And I'm now in 1650s and I'm the only country with the Quest for the New World NI, apart from Morea. SO I own the entire Americas and most ofafrica, except like, 5 nhlish provinces.
Is this a bug in the game/in my setting or does the AI sometimes just avoid colonization?
The AI does not usually vie for dominance of America, but will usually take random chunks out of it. The AI will take QFTNW, but it's main colonization effort will often be centered around colonise/conquer parts you have unveiled since your discoveries spread to the other europeans after 50 years (on normal settings).
Still, if you have not stunted the growth of the western powers, they will usually have spread quite a lot by 1650 -- rather, the Americas should be a patch-work of purple, red, blue and green. Portugal or Spain jumps on South America when their colonial range reaches that far. Someone gobbles up the Native Americans and someone does the same for Zapotec. However, if the player has already conquered every "visable" nation in north america it may very well slow down everyone else. After all, they'll have to establish conventional colonial range over the entirety of the Atlantic. Since you are Spain, South America is not initially colonized by an AI and you are obviously closest to it, by far. Your case isn't typical but it happens. It's not a bug. The AI is just not a perfect colonizer. Also, "lucky nation" sometimes fair better in this regard, but that is mainly due to a more stable home-front.
Added:
I just realised that I don't have that many late saves backed up, but to give you some illustration of the AI's capacity, look at this. Both are taken while playing outside of Europe, letting the AI do it's own thing. In the first, Europe entered a stable phase with the traditional majors taking control. Portugal and Spain moved into the Americas quite early and are soon coring their territory in 1523. They then extended their empire across the continent. In the other case, Europe disintegrated into a free-for-all melee, delaying colonisation until the range phase. Only a few island got colonised by 1590 and America soon became a patchwork of minor nations. In summery, the AI is always late compared to humans and will not partake in "planned" conquest.