Don't really know. But I think that, at least in the 90s and early 00s, there was a lot of property around, lots of choice, and lots of areas that were still a bit off the map for a lot of people (nkln was very off the map of most non-nkln-residents until as little as 10 years ago, I've heard, fwiw). Berlin has a pretty small population compared to its large geographical spread and I think there were always plenty of flats to go round. Apparently this is now not the case, it's now hard to find flats. I don't know if this means the population has grown, or speculators have snapped up the empty flats as they suddenly discovered that supposed no-go areas were really quite nice. Maybe it's still possible to get cheap accommodation in resolutely untrendy areas like Rudow, Koepenick, Marzahn......
Another factor might be that for a long time there weren't really any jobs in Berlin, no industries as such. So people who wanted to make money as opposed to hang out and go clubbing etc. probably weren't that attracted to it. Now Berliners are complaining that the place is full of "Schwaben" whom they view as particularly capitalist, whereas Berlin was traditionally insulated from the demands of capital.
On the 20th anniversary of the Mauerfall there was a survey that said that c. 20% of the population of Berlin wanted the wall back. That says a lot.