The only problem with running everything inside the event loop is when a task is doing blocking I/O, what most third-party Python libraries are doing. For example while requesting new information from a device, the core will stop running until we get a response from the device. To handle this, a task is able to suspend itself until the response is available after which it will be enqueued for the event loop to process the result.
For a task to be able to suspend itself, all code that it calls has to have this capability added. This means in practice that each device integration will need a full rewrite of the library that offers the integration! As this is not something that can be achieved, ever, a 100% backwards compatible API has been added so that no platform will require updating.
The backwards compatible API works by scheduling a task from a different thread and blocking that thread until the task has been processed by the event loop.
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