The problem is, as I noted: housing isn't everything. You need the support infrastructure as well to develop a new city quarter, and that's all but easy: you need schools and kindergartens with playgrounds (which consume a lot of space and create noise), shopping (at least a grocery store and a pharmacy), a general practitioner doctor, a bakery... and then, you need the "invisible" infrastructure that barely anyone thinks about: public transport, streets able to support the traffic that inevitably comes even with a good public transport system, larger streets in the surrounding grid, water and sewage grids, a power grid, heating grid.

The problem is, Munich got lots of new real estate around the city, but especially the public transport system wasn't expanded anywhere near close enough to what's needed. There hasn't been an actual new rail laid for the S-Bahn or the regional trains in decades (in fact, if you go to Mühldorf near Munich, the railway dispatch tech dates back to the era of the Kaiser, so even before Hitler and the Weimar Republic), the U-Bahn hasn't seen meaningful expansion in the core grid as well (only the leaves were expanded, in the late 90s to Messestadt, in the late 00s to Moosach).

And now, the road and public transport networks are at capacity. Munich physically cannot support more people moving here.