I'm leaving next week.
As shown here, the present progressive can represent an event that will happen in the future. I'm wondering what's the reasoning behind this feature.
The one I can think of is that in English the act of "leaving" can start when you've decided in your mind that you will leave or when you've arranged for your leaving, either of which can be some time (e.g., a week) before your actual leaving.
I'd like to know if native speakers agree with this reasoning. If not, please articulate what you think is the reasoning.
Both the Cambridge Grammar of the English Language (CGEL) by Pullum and Oxford Modern English Grammar (OMEG) by Aarts clearly say that the progressive futurate (i.e., the present progressive indicating a future event as in I'm leaving next week) does not have a progressive meaning to it.
OMEG on page 270 says:
It is important to be aware of the fact that [the progressive futurate] is not aspectual, that is, the situation is not regarded as unfolding over time.
I'd like the answers to be in accordance with this analysis that the progressive futurate is not aspectual.