They don't even own the buildings, they just lease the space. That shows you how screwed up Silicon Valley Valuations are.
My company needed to lease out space there for a few months not too long ago and we really liked the space. The service was good, (TBH they weren't really designed to handle the needs of a non-startup company).
The best way to describe it, WeWork takes the old "business centers" and combines it with the coffee-shop which will let you sit all day, with some business programming.
It's a really well-executed idea, but the valuation on it makes less sense than Uber.