When Colombus landed in the Americas, he had promised Isabella and Ferdinand riches. If he didn't deliver, things did not look good for him. So Colombus vastly exaggerated the wealth he found, and heavily publicized his exaggerations. A very large number of copies were made,
some still extant. And they got spread around Europe pretty quickly, creating an -at that point- totally unwarranted impression of the Americas as full of riches (and next to China). Colombus later lucked out again in that there was actually loads of gold.
If the first contact had been someone who didn't have two warrior-monarchs breathing down their necks and tapping their feet, going "Well?" (figuratively), Europe's first impression of the Americas would have been as a much less interesting place.
Also, Columbus and Iberia was not a good place to be discovered from, geographically. It meant that the Europeans established themselves on the islands of the Caribbean, where they could easily reach the large native polities, but could not be touched in return. They cold sail straight to Mesoamerica, and the plagues hit the heartland of the Americas first. A different discovery would probably have seen Europeans initially working their way up from Brazil and down from Newfoundland. While the Amazonian nations would still have been toast, the Incas and Mesoamericans would not get the plagues and the conquistadors at the exact same time, but with some years between them.
Of course, things would still have been terrible for the Americas, but at least they would have had plagues and invasions separately and not at the same time.