The answer to this can be found in Chapter 18 of the book. Specifically, it can be found on pages 370 through 374 in the paperback edition. Basically, the greater success of the Europeans who came after Columbus can be explained by geography and by timing.
Geographically, the Norse explorers came from a less ideal part of Europe and they came to a less ideal part of the Americas. They came from areas of Europe that did not have large enough populations to sustain colonies far overseas. They came to areas of the New World that were cold and not very good for farming. By contrast, the Spanish came from a much bigger country with a larger population. They also came to a part of the New World that was much better suited for agriculture.
In terms of time, the Norse came too soon. They came at a time when European technology was not as advanced. Their ships were not big enough or fast enough to really supply their colony from Europe. By contrast, the Spanish sailed at a time when ships were bigger and faster and when European weapons were much superior to what the natives had.
For these reasons, the Spanish colonization was much more successful than the Norse efforts.