In Germany, there is also a problem that many of these new lines are expected to have mixed traffic on them, meaning both fast passenger trains and freight trains. This makes them much more expensive than they would have to be, as both types of traffic have quite different expectations. Passenger trains need curves with very large diameters (~ speed^2 relation, even 7 km diameters) in order to allow the high speeds. Freight trains aren't that fast, so they don't need such a large diameters of the curves, but they can't handle as steep gradients. 4% slope is perfectly OK for an HS passenger train, but at least impractical for a freight traffic.
French HS train lines are for passenger traffic only, they can be (and are) built adjacent to existing highways and so. And of course. They are built as whole new lines, instead of the (not only) German patchwork.
Btw. you are missing HS railways in Spain, where it is built in a similar manner to France, there are already complete operational routes, and the service seems to be very successful as well.