I am really surprised. Things are going well for them as a company. Why do they want to screw it up for themselves?
I think there was just this notion that you can promote from within to get your leaders... but this only works in some cases. Those directors at "stuffy" corporations like Oracle/Cisco/Microsoft? Fact is, they know how to manage teams at scale and you need some of them in your organization as it gets bigger. Even if the environment gets a little more bureaucratic.
Just look at the Frightful Five. At least two of them are renowned for having brutal, sometimes abusive, corporate cultures. Three if you include stack ranking-era Microsoft. Having an awful culture doesn't preclude business success.
So yeah, there's plenty of finance firms, VC backed unicorns and Fortune 500 behemoths with lousy cultures. But I'll bet that the cultures weren't that toxic _for the initial employees_.
NB People are different. What's toxic for one person isn't for another. However, in large firms the law of large numbers means that toxic looks much the same. So you can start a firm with founders and initial employees who are shouty abusive a-holes and it's not a problem. Scale to a thousand employees and it most definitely is.