It costs more to train a pilot to fly from both seats, so why bother? Particularly with the barely-trained co-piglets struggling onto the OCUs these days. Something which is NOT their fault;
QFIs fly from either seat - bacause of their naturally superior skill, of course!
There is no need to train both pilots to fly from either seat - particularly when, in proper aeroplanes, it's possible to operate the whole trip from either seat.
Don't listen to the kipper fleet - they let AEOs and even navigators play at being Captain..... No stick, no vote!