First you have Price's Law - half the people actually doing work rises with the square root of the total employee count. It's a variant of Pareto law. So as you grown bigger, the critical path of viable operation depends on fewer and fewer people per capita.
That group is also the group who first to see problems and least likely to put up with BS so they are the first to leave when things go downhill. The bigger the organization, the fewer people who need to leave to destroy it.
This is one of several dynamics that assure a role of startups and entrepreneurs because large companies can never be safe or stable or eternal.
Related to this: most startups last no more than 5 years but large corporations seldom live beyond 20-25 years. The handful of corporations that do are super rare and mostly living on borrowed time. Usually the only thing keeping larger companies around beyond 20-25 is one or a few very charismatic leaders/executives - as soon as they go, it comes crashing down. Hewlett-Packard is a classic example of this.