Many of those who survived in Britain were taken to the film's setting. It's more or less a big screw you to anyone who saw the first film because it means that the first film's protagonists presumably were there and almost certainly were killed if they were there. It more or less makes the whole previous film a huge waste of time following characters who were going to die anyways.
There's no guarantee that the protagonists of the first movie would return to the UK after being evacuated. And indeed, given how 28 Days Later ended, the chance that any of them would be willing to live in a military-run quarantine zone is effectively nil.
The Infected in France. Think about that. The Virus decimated Britain in four WEEKS. It would spread like wildfire across france, it's neighbouring countries, and eventually Europe, Asia and Africa with only a few areas (the poles, the americas, the asian islands, Australia, New Zealand etc) clear of Infection.
A disease that virulent can't spread too far before burning itself out, in real life at least. The Infected don't show any incentive to move long distances unless they are chasing after people, so the chances are that after the biggest population centers are clear of the uninfected in one way or another, it becomes a waiting game, and normal people come out on top. Ofcourse millions would likely die before that would happen, ofcourse.
How is that Fridge horror? That is the entire point of the ending. They wouldn't have SHOWN the Eiffel Tower otherwise.