Not many people would be willing to climb stairs to get to the twentieth floor. Some people (e.g. my very sedentary and morbidly obese grandmother) wouldn't even be able to do that.

It's interesting that the creation of a social awkwardness device is essentially the only reason we have high-rise buildings in the first place. Note that malls, which must make significant efforts to attract people and make them feel comfortable (and ready to spend money), either make limited use of elevators or actually do make them transparent. Escalators wouldn't work for anything more than a few floors. Like you mentioned, stairs don't work either. We need levitation (or at least pneumatic) tubes!