Just as with many highly valued startups, you can think of WeWork as valued for the possible future business model rather than it's current one. If WeWork is able to transition to a business services company with essentially a captive market (its tenants), it'll be a very profitable company. Other such companies have a high customer acquisition cost. WeWork is betting it's more efficient to rent office space and have a mailing list than to pay Google for those same eyeballs.