The post you are reporting:
Southampton's Cruise market is entirely different from Dover's. Not only do they have 'cold water' & Mediterranean cruises, they have the long haul, trans-atlantic and worldwide cruises that attract a different class of money. On my last visit at the end of May, there were two Cunard "Queens" ready to depart, as well as half a dozen other liners - a little different to our maximum of two liners at any one time.
Southampton's Town Centre is just as unaccessible by foot from the terminals as Dover's is, probably more so - but then it is a busy University city. What it does have in abundance are chain Hotels close to the seafront to suit all budgets.
If Dover was Canterbury-by-the-sea, the cruise customers would stay here to explore, as it is we don't have the perceived "Charming English City" status that cruise customers expect.
I'm sure that will create outrage in some quarters, but that is the hard, blunt truth. Dover needs to come up with it's own USP, rather than moan, or try to compete against Canterbury.