My reasons are based off the effect of Roman conquest in Europe.
1. The Romans brought a system of learning that is the basis of most of Europe's languages. This common tongue allowed the faster development and spread of technology.
Latin-derived languages are spoken by less than a third of all currently living Europeans/Mediterranean people whether you only take Europe or the former Roman territorry, and way less than that if you take both.
The linguistic barriers weren't a dealbreaker in the middle ages though. Scholarly languages (Greek, Latin, Arabic) were sufficient to spread knowledge through the writing classes without the populations at large being remotely familiar with them.
Likewise they weren't a dealbreaker for the ancient Mediterranean even though Greek/Aramaic/Punic/Latin speakers were not necessarily dominant in numbers.
There was a common cultural space in the Med including parts of Barbarian Europe, just like there was a common cultural space in Mexico, Guatemala etc. despite linguistic differences.
There was no common space between the Mesoamericans and the Andes.
2. Those that hoped to avoid war or defeat the Romans had to start buying their weapons. Those that were conquered adopted these weapons into their culture. For the Inca in this scenario it would make them very rich, as Amazonian tribes and even as far as the Maya and Aztecs began to buy or look for copper mines of their own.
The Romans took the scutum and the hasta from the Samnites, the helmet and the Gladius from the various north Italic peoples, the long spear from the Greeks, the falcata from the Iberians...the mail from the Gauls, the breastplate from the Etruscans, the Trireme from the Carthaginians and the Greeks...the Romans arrived into a world firmly in the Iron age and their innovation was probably organisational. The uniquely Roman things are (maybe) pila, 3rd c. matriobarbuli, and perhaps the segmentata (1st-3rd c. CE).
It's not a directly comparable situation.