good question...i don't know the ins and outs of it but from memory some of the factors were...
the husband/part owner? was killed in a top dressing accident in marlborough but i can't remeber if this was before or after they stopped operating...
fast ferries/cheap fares...
porirua harbour/lagoon wasn't exactly an ideal place to land for travellers/suits
i do remember at one point there was a hottie working for them in picton and whilst waiting for the ferry i asked if i could see her beaver (or sumthing along those lines) i just got a wry smile like she'd heard that line a hundred times before.