Leaders influence company culture but it's also a self-feedback loop where leaders that fit the company culture end up being leaders in the first place. To break that feedback loop and change course is usually a conscious choice for a company. Even then leadership change and direction at the top is only one of the many signals. It's entirely possible for Zoom's CEO to be a security minded person and the PM/Infosec person who reviewed the security report decided it's not a flaw worth patching.

Slow degradation to industry standards is the norm not the exception. That accelerates with growth as the original culture gets diluted.