According to Guns, Germs, and Steel, why was it too late, for the crops of the Mexican trinity to grow, when they arrived in 1100 A.D.?
It is not completely correct to say that it was too late for the plants of the Mexican trinity to grow in what is now the United States. Instead, it was too late for the Native Americans to build a civilization upon those crops when they arrived in 1100 AD. The reason for this is that the Native Americans had only a few hundred years left before the Europeans came. That was not long enough to build a civilization that could rival one that had been growing for thousands of years longer.
In Eurasia, crops were (as we see in Table 5.1 of the book) domesticated as long ago as 8500 BC. This means that civilization in Eurasia had been growing for 9600 years before the Mexican trinity ever got to the Eastern United States. It is surely impossible for a civilization to grow in 400 or 500 years that will be able to stand up to one that has been growing for 9600 years.
So, the real problem here is that the Europeans had too much of a head start. Their civilization had been developing for thousands of years and the Native Americans would have somehow had to catch up in only 400 years or so.