According to Diamond, Eurasia developed more and better technologies than any other continent because of two major factors.
First, Eurasia was able to develop agriculture early on. We know from other parts of the book that this was due to the fact that there were more kinds of plants and animals in Europe that could be domesticated. Because Eurasia got agriculture so early, it was able to develop the sedentary societies that make it possible to develop technology.
Second, Eurasia has a long East-West axis that is not really broken up by any geographical features that make travel difficult. This meant that there would be many cultures, relatively similar to one another, and relatively near to one another. These societies could trade technology with one another. This would help Eurasian societies develop more kinds of technology.