After sufficient time has passed, every company will need a new CEO, as no CEO lives forever. Each new iteration of CEO, whether internally or externally recruited, will bring a fundamental change in dynamic. You simply can't guarantee that the next generation will have the same values, views, and ways of working as the previous.
The CEO of a different company in charge isn't that different than an internally sourced CEO in charge.
I think the difference is that when you have lots of duplication (of systems, departments, job functions, processes, etc) like after an acquisition, there is very tempting low hanging fruit there for a CEO in a cost cutting frame of mind.
If you want to boost numbers this quarter and don't care too much about intangibles, the incentives really push towards gutting the acquisition.
A CEO of an independent company has different incentives to a CEO of an acquirer.
A company culture is a reflection of the company's leadership.
The culture of Microsoft has gone through radical changes between gates, balmer and nadella.
But a culture isn't _only_ a reflection of the leadership, it's all the interconnections of people and organizations within the whole company.
A leader can come in and make changes, and often these changes first have to break everything that's there already; without care what replaces the broken structures is just chaos; by default that chaos is the governing culture without more inputs and work from leadership.
These changes are most pronounced when 2 large organizations become one because both cultures have inertia (whole foods / amazon, slack / salesforce, etc). But yes, of course when CEOs change there's change to the corporate culture, but because there's only the force from the CEO's changes not entire cultures bashing into entire other cultures, the changes tend to be more gradual.
I am not an MBA or sociologist or really anyone with a worthwhile opinion, I've just been around the block and have the stories to tell or retell...
It’s a fundamental change in dynamic.