IMO (based admittedly on somewhat limited knowledge of pre-contact American history/cultures) it had a lot to do with isolation. We tend to think of Europe as a continent, but really it's the western end of the Eurasian continent, plus being right next to Africa. There's no long sea journeys needed to get from Spain to China, to Ethiopia, to India, etc. This allowed technologies and ideas to spread - by multiple means - over the millennia. Some were brought by settlers/migrants, some by traders, others by invading tribes, etc. So the technologies were known, to a greater or lesser extent, to more people, which gives a higher chance of someone developing each technology just that little bit further. Someone up-thread mentioned contact producing rivalry and spurring further tech development, which is another strand to the same kind of argument - in other words, if your enemy (or even just rival) has something which is making their army fight better / goods sell better / farms produce more / etc, then you are more likely to try to copy it, with the concomitant potential that you will improve it or perhaps find an alternative which is even better than what your enemy/rival has. There just wasn't the population density/pressure across the entire American continent(s) to force that same exchange/development of ideas. It's notable, to my thinking, that the most advanced civilisations in the Americas were where the greatest population pressures were - meso/central-America.
I guess you could summarise my thoughts by comparing three land-masses:
1. Eurasia-Africa - lots of people, lots of wars and trade - high tech
2. N/S-America - not so many people, fewer wars and less opportunity for trade - lower tech
3. Australia/Oceania - very few people, far fewer wars and much less opportunity for trade - much lower tech.
Yes, there are other factors (terrain, animals able to be domesticated, etc), but my personal belief is that it's population density/pressure/exchange which is the root cause of the tech difference(s).