I think many of those people are on-site staff for all the office space. Sales, security and maintenance mainly. The space you rent from them is managed. The basics are provided by them: power, networking, janitorial, heat, shared kitchen with coffee and other stuff etc. Direct WeWork employees take care of most if not all of that crap.
My current employer was located in Wework space for the first 18 months of business, until we grew out of it. You can rent anything from shared space access (cheapest) to as many desks as you care to pay for.
Full disclosure: I do not plan to invest either. Just relaying my experience.