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.
Not even the Americas would be safe, really, considering that it wouldn't be impossible for the Infected to make it across the Bering Strait and begin spreading Rage across North America.
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.
While true, a disease that virulent would normally KILL the infected but the Rage virus doesn't. Assuming that they die from starvation or dehydration, the time they could spread the disease would be at least a week or longer (based on the logic of the movies).
How is that Fridge horror? That is the entire point of the ending. They wouldn't have SHOWN the Eiffel Tower otherwise.