Lots of info from people who know the region (3 days old): https://www.youtube.com/watch?v=SJ6YliBbvII

Several speculations in that video:

* Erdogon knows Trump will pull out of Syria and is trying to place himself as the power that will "take over" from the US.

* Israel wanted these forces to come down and surround the inner border of Lebanon in order to cut off arms moving to Hezbollah, so Israel jointly worked with Turkey on this.