A big impediment is the federal structure of Germany, as high-speed trains need to have at least one stop in every federal state they cross for political reasons, which of course makes them slow.
That's not generally true. For example, the ICE train from Hamburg to Berlin goes through 3 other states (Schleswig-Holstein, Mecklenburg-Vorpommern and Brandenburg) without stops.
There may be local politicians in some states making such demands ("If you want to build your tracks through _my_ state, ..."), but I would assume they are trying to make an impression in an election campaign or something.