P and O have always said there were issues with the vessels width restrictions at Hull due the size of the lock meaning they cannot use a vessel the size that they do on the Rotterdam route.
The Pride of York and Bruge were due to be replaced as in recent years they have had expensive breakdowns and the other option would be a new facility alongside the one for the Rotterdam ferry in the main river channel .
Case of cutting their losses, wouldn't care I still have a credit for a trip and even last week they told us that bookings for the Hull to Zeebrugge would be available for next summer from 1st October 2020