To many people, being in a startup is about selling the same thing to the same people - eyeballs to VCs or Google. That's it. There frequently isn't a lot of concern over what exactly it is that draws them there. In these situations, long hours are required (or at least mandated) because the target moves so frequently because someone has a "better idea" or needs to implement "just this one thing" to appease some VC who ends up not funding you anyway. This lack of focus and constraints leads to middle of the road products that can only be worked on by people working 14 hour days to adapt to the ongoing changes.
It's sort of like when Hollywood is out to make a "blockbuster." They buy a popular comic book character, get a dozen hack writers to work on it - even while the scenes are being shot - and they put in a bunch of crap special effects. Sure, sometimes it works, but most of the time it's a bunch of dreck that will never make back its $200 million budget. Contrast that to the lifestyle business - er, independent film - being written and directed by the guy who LOVES what he's doing and making it for himself and you get Pulp Fiction.
Me, I'd much rather make "Pulp Fiction" than "Daredevil."