Too often the people at the top don't define the culture explicitly. Instead, they do it accidentally through behaviors they incentivize, often without even realizing it. Sometimes they do this in direct conflict with the culture they are trying to explicitly champion (e.g., saying "we believe in transparency" while subtly punishing people for being open, maybe for well-intentioned reasons). And once a given company culture takes hold, it can be very hard to change because people who thrive in that culture tend to stay longer and get promoted more. Those people end up being a kind of "momentum" for the proliferation of said culture.
In my experience, it takes people in positions of power, and with real skills for cultivating culture, to deeply change an existing work culture for the better. I've seen a few leaders with such skills make wonderful changes at their scale of influence. But I've seen far more people in leadership positions who act as if they are largely unaware of the nuance and importance of good company culture.
Such changes are also hard because meaningful cultural improvements often conflict with short term revenue/profit. It takes a lot of discipline in senior leadership to maintain the needed resolve given ever-present pressures to produce in the short term.
In my experience, it takes people in positions of power, and with real skills for cultivating culture, to deeply change an existing work culture for the better. I've seen a few leaders with such skills make wonderful changes at their scale of influence. But I've seen far more people in leadership positions who act as if they are largely unaware of the nuance and importance of good company culture.
Such changes are also hard because meaningful cultural improvements often conflict with short term revenue/profit. It takes a lot of discipline in senior leadership to maintain the needed resolve given ever-present pressures to produce in the short term.