Both Southampton and Portsmouth do have developments like this though. They're just not that out of town.
Southampton has that leisure park where the cinemas are, Ocean Village, and Portsmouth has Gunwharf Quays.
A lot easier to build in those places because of all the brownbelt land. These cities are port cities so have a lot of industrial sites, many of which are more valuable now as leisure, shopping and housing developments. By contrast Brighton is a seaside town for tourists, so we don't have anywhere near as much big industrial space that we can now build over
Agreed. They are absolutely NOT 'out-of-town' shopping developments. In Southampton's case, the shopping development is West Quay, which could not be more town centre. The two other sites (both ex docks /industrial) are Ocean Village, and the one you probably meant (with the Odeon Cinema) Leisure World, are both just food / cinema / casino - not shopping. Gun Wharf is a discount outlet / food / cinema / housing development (and a pretty good one). What TCB is referring to is a Bluewater / Lakeside / Meadowhall kind of set up.