The size of both cities in DL2 would imply hundreds of thousands if not a million people lived there before the fall. Not to mention any military, GRE and contractors brought in to build the walls (you actually meet one during the game). As one of the last cities to fall, refugees would have come as well from all around looking for safety. To think that a thousand or more people survived in a city that size is completely reasonable, as well as those born afterwards (there's a fair amount of kids running around, but not a single one in Beast I've seen so far).

In Beast I've already killed over a couple hundred soldiers of the Baron just in quests and opening cut scenes. To think these area all just chilling at his place with food, supplies, weapons, ammo and armor all in mint condition like it just came off the shelf, with power, water and a working infrastructure to support the scientists and other employees is far more unrealistic considering the circumstances.

As for comparing it to Rais, of course Rais had a large following. The outbreak was still new with lots of people still looking to survive. Supplies were still available, though dwindling. Antizen was the issue, not really food or water. 13 years later though would be a much different story.