Because coworking spaces are full of employees of other companies, while working cafes are usually solo people working in super focussed fashion. There's no foosball table. No startup kool-aid. It's the same with private members clubs. Usually it is the founders, investors, lawyers, reasonably successful people in whatever field they work in. The networking opportunity is immense, and it's usually a better atmosphere.

I'm sure a coworking space could maybe screen their candidates and employ a deep work culture. But so far they are focussed on free coffee, big TVs with Playstations, beer on tap and ping pong tables.