I don't know enough about the 'behind the scenes' to give an accurate answer. Perhaps something to do with there only being 3 787 bases? The junior guys are taking a UK base in the summer and Scandi base in the winter. I guess the older FOs with families don't want that and are waiting for permanent UK slots to become available. I'm just guessing.
It's not a bad way of life at all. Very senior fleet for the LHS.