Because I find the "normal" behaviour of Kedro, which defines a global session ID for all nodes, very useful to see at a glance which run produced which dataset and be able to link all the datasets in my output folders.
With Airflow, I ended up with versioned datasets having different run IDs as folder names....
I know that this is not the way it works with Airflow because, as you said, a new session is created for each node, that's why I wanted to find a way to somehow override the save_version of each dataset.