I suspect it was just the zeitgeist (+ also ease of the recorder)- if you look at early wills deeds etc you can see the almost equality of the man and woman's family names eg the woman might sign her family name first followed by als married name - this disappers more quickly from the towns as the english custom (women as per Roman law are chattels of the man) takes over - it has been argued by lawyers that Manx law reform post 1765 saw a continuous removal of woman's rights - not corrected until early 20th C