Because Germany is mostly old money, inherited for generations, that is very risk adverse so instead of investing it in new SW companies or buying stocks, they park it in real estate in desirable areas and prop up this bubble since it's a sure bet for a return on investment. That's why they call it Beton Gold ("concrete gold").
Munich has very strict limits on vertical height so that cathedral spires aren't drowned out by the buildings. On the edge of the city you do see some taller office buildings but not in the core, and certainly not to the extent you would expect in a major city.
