> Look at the data passed to the event. The callstack starts at the function attached as a listener to the event.

> Is the event data incorrect? Then the problem is in the code that triggers the event.

> Is the event data correct? Then the problem is in the code listening to the event.

It's difficult to reason about the event triggering code when it's call stack is not available. For a larger code base where an event is trigger in multiple locations with different logic in each location, it may be difficult to pinpoint the triggering code, let alone reason about that code. Direct function calls are much easier to debug because you can walk up the chain of calls and inspect the variables and state of each frame.