i can think of two reasons from the top of my head. first, when germany and berlin were separated for decades, the east was vastly neglected. after the wall came down, huge amounts of east germans moved to the west all over germany - thus leaving berlin sort of empty and with an abundancy of space and real estate. second, having been mostly isolated after ww2, german banks and heavy industry etc settled anywhere but in berlin. economically, this still hurts berlin today. culturally, this makes berlin more of a place for creatives and free minded people who create their own paths rather than corporate suits. i'm building a startup here and it's an amazing place to be!