I would think that as they were possibly two of a very small number ( L.T.U. being the others) that were in all tourist configuration. Many of the "majors" would be reluctant to take on 2 non standard aircraft. Were the airstairs unique to Court's twins ? For an I.T. operator to take on the huge costs of training/ support must have been daunting at the time.
Hope it helps
Be lucky
David