People already knew what kind of business WeWork was. Sure, they were getting press, but when actual institutional investors looked at it, they must not have liked what they saw.

That has been going on for the last few rounds, so I suspect that they couldn't have gone public then, either. Nobody was buying what they were selling, except Softbank. And once the S-1 dropped, the press and social media saw all the red flags together in one document.

Those red flags would have been just the same if they'd gone public earlier.

Can you give some examples where this has worked in the past?

The alternatives are either that Softbank believed in WeWork's fundamentals, which honestly feels unlikely, or to believe that they went in early, then discovered that nobody else would invest, so they kept putting more of their own money in to avoid closing the business and taking a write-down.