In fact, the Incans did know about wheels, it's just that wheels are considerably less useful when you don't have any large pack animals to pull things.
The Incans did not have the wheel (when we refer to people having the wheel, we mean with an axle). They used wood beams to roll things around, but that's not a wheel. As far as I know, the only group that had the wheel in the Americas were the ancient Mexicans.
Further, devices like wheel barrows and carts are incredibly useful with or without pack animals. Doubly so if you had the incredible manpower that the Incans had where you can easily just use humans to pull them instead of pack animals. Wheels aren't just for hauling things around either, it is hard to express how incredibly useful potter's wheels has been for the last five thousand years.
To be honest, I've always found the evidence that ancient Mexicans had the wheel rather dubious. All we have that supports this claim are small clay fired figurines that allegedly had wheels on them. The problem with the claim is that the axles would have been made of wood so they no longer exist. So all you have are some clay fired figures with 4 round disks... If they really did have wheels, then it's rather mind boggling (and rather implausible) that they didn't apply the technology to something more practical.
I think it's important to approach history/art-history of ancient cultures with a health dose of skepticism - especially ones that didn't have a written language. These academic fields sometimes promote theories that are based on rather wild speculations.
I think Incans lived in the mountains and lacked lots of flat ground with which to roll things around. So they did develop some wheel-like devices, but they never applied them in things like wheel barrows or carts because those are just not that useful going up and down mountains.
On well worn paths on moderate to even heavy inclines, a cart is still highly effective at reducing manpower necessary to move heavy objects (like the giant stones the Incans moved).
The Incans didn't not have the wheel because they wouldn't have found it useful. The Incans didn't have the wheel and axle because it wasn't an obvious invention.
All evidence points to the wheel in the "old world" (ugh, I hate that term) being invented in one place at one time. It wasn't obvious. It wasn't simultaneously invented by hundreds of people across Europe, Asia and Africa. It was simply copied everywhere and Europe, Asia and Africa were fortunate enough to be connected.
It's not a bunch of jagged rock. The Altiplano, where this bridge is built, is a plateau between two parts of the Andes infilled with sediment over the past 30m years. Wheels would be quite useful there.
The Incans did not have the wheel (when we refer to people having the wheel, we mean with an axle). They used wood beams to roll things around, but that's not a wheel. As far as I know, the only group that had the wheel in the Americas were the ancient Mexicans.
Further, devices like wheel barrows and carts are incredibly useful with or without pack animals. Doubly so if you had the incredible manpower that the Incans had where you can easily just use humans to pull them instead of pack animals. Wheels aren't just for hauling things around either, it is hard to express how incredibly useful potter's wheels has been for the last five thousand years.