Well, Buurtzorg is a large organization, it's just that it does not have a large hierarchy. I suspect you're really asking "high-trust" and "large hierarchy". In that case there's plenty of causes to point at. I'll just give a few of the top of my head
First, note any organization that breaks into different departments (hierarchical or not), at least partially does so to let each department "abstract" away the other ones - if you don't have to worry about issues outside of your responsibility, you can focus more on yours. That is actually a form of trust.
In the case of a hierarchy however, that means that each layer abstracts away the layers above and below, and since going up multiple levels in the hierarchy happens indirectly, the further away, the more abstract things become. So that often needs some kind of structure to regain the trust that is lost by dealing with abstract departments - leading to bureaucracy.
On top of that, usually more power resides higher up the hierarchy. That means that without explicit structures to compensate for this, people lower in the hierarchy lack individual leverage to protect themselves against bad decisions made higher up, that may not even be malicious or intentional but just a consequence of the aforementioned abstraction.
Of course, most structures that are created to fix this typically are also abstract procedures, meaning they barely help with our instinctual "I cannot attach a face to this" type of distrust. Bureaucracy can create leverage, but rarely creates trust. Which also explains that quite often, talking to someone in person can make such a difference in being allowed to "go ahead" or not. Because it can provide a more "natural" sense of trust that bureaucracy is supposed to provide but barely does.
First, note any organization that breaks into different departments (hierarchical or not), at least partially does so to let each department "abstract" away the other ones - if you don't have to worry about issues outside of your responsibility, you can focus more on yours. That is actually a form of trust.
In the case of a hierarchy however, that means that each layer abstracts away the layers above and below, and since going up multiple levels in the hierarchy happens indirectly, the further away, the more abstract things become. So that often needs some kind of structure to regain the trust that is lost by dealing with abstract departments - leading to bureaucracy.
On top of that, usually more power resides higher up the hierarchy. That means that without explicit structures to compensate for this, people lower in the hierarchy lack individual leverage to protect themselves against bad decisions made higher up, that may not even be malicious or intentional but just a consequence of the aforementioned abstraction.
Of course, most structures that are created to fix this typically are also abstract procedures, meaning they barely help with our instinctual "I cannot attach a face to this" type of distrust. Bureaucracy can create leverage, but rarely creates trust. Which also explains that quite often, talking to someone in person can make such a difference in being allowed to "go ahead" or not. Because it can provide a more "natural" sense of trust that bureaucracy is supposed to provide but barely does.