This has more to do with the farce that they found themselves in when procuring a new booking / ticket/ revenue management system they're calling "Ar Turas".
STATE-OWNED ferry operator CalMac has defended a further delay of the launch of its £18m booking and ticketing platform - ten years after it was…
www.heraldscotland.com
Exclusive: The Scottish Government-owned ferry operator is launching its Ar Turas ticket booking system later on this month which will replace the ageing old one.
www.scottishdailyexpress.co.uk
Essentially, they want full end-to-end control of their sales processes and customers - third party points of sale like ScotRail / wider rail industry etc don't fit into this. If they've got any sense, (they don't), they'd create a generic discount/promo voucher code that allows you to book a reservation/ticket for a sailing on their new system- but with a requirement to produce the rail ranger/rover ticket when checking in/boarding.
I think it is somewhat outrageous that Scottish Government haven't intervened here - but I think the severe and prolonged issues with the booking system have probably made everybody very weary, especially at a time that the Scottish political landscape is so bad.