A dictionary says:
sky·walk (skī′wôk′) n. An elevated, usually enclosed walkway between two buildings. Also called skyway.
I will not comment on the use of skyway vs. skywalk, that’s just like Ramp and Garage.
While I point out that streets steal urban activity from the skyway system, they seem to feel the converse is more relevant. Yet who is to say the street level should be for people not cars? Why should humans lower (one might say degrade) themselves by letting mechanical vehicles share their space. Why shouldn’t they rise above, as Leonardo DaVinci would have them do (Figure #0)?
Certainly, it cannot be roofs that urbanists object to. Almost all of them live in shelters with roofs. They all advocate roofs for their mass transit vehicle. So what is special about the short trip between their shelter and their vehicle, that it must remain unroofed.
Further it cannot be the lack of vehicles, many urbanists like pedestrian zones so long as they are dominated by pedestrians. (Jeff Speck and others seem to want cars in their shopping districts though).
Perhaps it is their tubular nature? Maybe urbanists hate tubes (and gerbils?). (In Atlanta, I have heard the skyways referred to as “Honky Tubes“, so there are clearly racial overtones). They are a bit minimalist, not the lush environment some may seek. But that is simply a design choice.
Perhaps it is elevation? But most urbanists think something like the Vancouver SkyTrain is a good thing, and support transit with grade separation so it can go faster. Why not people? [I fully understand not liking forcing pedestrians onto a pedestrian bridge as is common in China, so that walkers and cars are separated, but the pedestrian must climb and descend a staircase, but that is not the case here]
Perhaps it is ownership? But most American cities grew rapidly under an era of private transit (in the Twin Cities through 1969), so what is public vs. private space is also ambiguous. Streets are more clearly public, but if I let people pass through my buildings, seems a good thing for the public, no? If they were all publicly owned, would it be okay then?
The question “what is a skyway?” cannot be easily resolved with words alone. These Figures (1-3,5) from Vienna, Austria, Figure 4 from Stevenage, England illustrate the problem. Figure 1 is what urbanists have in mind. But what about Figure 2, Figure 3, Figure 4, Figure 5. When does the cavity under a bridge become a tunnel?
Why are 1 and 2 bad but 3, 4, and 5 good?
London Bridge is another example, the other way about. It is a skyway of sorts, a bridge over a river with buildings on either side (though not at the entrance to the bridge).
Pedestrians without the bridge would need to swim, ferry, or walk on water. The pedestrian traffic attracted business, so it went from a typical bridge for movement (a skyway over the main transport artery in London) to a mostly-enclosed bridge with shops. Is this good or bad?
The Washington Avenue Bridge over the Mississippi River is now truly multimodal, with a lower deck for cars, buses, and LRT, and an upper deck for pedestrians and bicyclists, with an [rotting, smelly, but warm] enclosed section for pedestrians. Is that deck a skyway? Obviously the aesthetics are no London Bridge, but is it inherently bad, or just poorly executed?