If there were more housing close to those skyscrapers; if it were legal to build it, those people would have shorter commutes - and occupy less land to boot.

Instead, San Fran is one of the NIMBYest cities on the planet and so all those people are forced to come in from further afield.

The skyscrapers themselves are pretty eco-unfriendly as well, frequently built as essentially a giant greenhouse with heavy heating & cooling loads to maintain comfort.

I suppose you might look at some technical discussions of whether you're better off with a larger area built up to 6-10 stories or something like that, than fewer, taller skyscrapers, but in general, that denser environment keeps cities from sprawling out, and is more friendly to people walking around.

I prefer the more European style of 2-8 stories, like here: https://goo.gl/maps/poabxNny8r8Jq46v7

But I think the broader point stands.

Many european cities max out at 8 stories simply because they were built before the advent of elevators, or the design aesthetic started before the elevator and they're keeping new neighborhoods consistent.

4 floors is mildly inconvenient on foot but 8 floors is becoming a real chore for people over 40.

Almost no buildings beyond 4 floors (5 the way Americans count them) lack elevators in Germany or Austria at least. I suspect it's the same elsewhere in Europe.

That seems counterintuitive to me. I'd expect only having one or two walls exposed to the outside (maybe 3 if I'm on the top corner) would reduce the amount of energy I lose to the environment compared to a house with 5 sides exposed. Plus a skyscraper can use a larger and more efficient system than a single family home.

Right, but your family home is likely insulated to at least R-13 in the walls and R-38 or better in the attic while an all-glass skyscraper is probably something like R-2. A tall & thin skyscraper also has an uncompelling surface to volume ratio.