Sorry again Harry, but comparing Ostend with Luxembourg is not exactly like for like is it? There are many better places than Ostend as there are many better places than Luxembourg (which I know well too btw), such as where I live for instance
The point is that Ostend offers access to the Belgian coast and other areas, both of which have been and continue to be very popular with British tourists. It's a pretty long trip from the north of Britain by land and sea. Arguably an OST route from northern UK could perhaps work if well promoted and seasonal. One thing is for sure, with all the beautiful places along the Belgian coast, tourists would not be restricted to staying in Ostend itself.
It would also be critical to operate such a route with the right equipment. Ryanair failed with Ostend just as they did with Maastricht because neither route could sustain 180 seat 737s on them.