Yap saw that first hand. Someone read too much HN, wanted to run a startup. They didn't even have a good idea, but that didn't stop them. However, the was a minor problem and that was they needed investors.
Well as it turns out, if there are investors who are even more stupid than the founders and are willing to bankroll that, it's not all bad. Just take their money. Convince them you could be the next Facebook, look at the billions Facebook made!
So the startup is just a proxy to take investors' money, and play CEO for a while, and then when it fails it becomes a resume line "CEO at Uber For Dogs inc."
And yeah they didn't really have an idea, they just sort of came up with on, basically what they thought investors would like. For example, say, investors liked dogs, so the idea he came up with was Uber for dogs.