To some extent this simply reflects the real differences in population distribution between Germany and France.
The urban agglomeration of Paris houses roughly one sixth (!) of the total population of France, and is roughly 6½ times as big as the next biggest agglomeration (Lyon).
The biggest agglomeration area in Germany in Germany (the Ruhr area, which in turn is itself somewhat spread out and rather polycentric even on the local level) on the other hand only accounts for slightly more than 1/15th of Germany's population, and going further down the list you won't find any such large size discrepancies as between Paris and the rest of France. (In France, Paris is the only agglomeration area with more than 2,000,000 inhabitants, whereas Germany has seven agglomeration areas of that size category, all spread out throughout the country.)
So in France it totally makes sense to just build a series of radial high speed lines all linking Paris with the provincial agglomerations, and even where one line might serve several cities along the way (like how going to Marseille you also pass through/next to Lyon), traffic to/from Paris will dominate, so you'll still get lots of non-stop Paris ↔ Province trains and only comparatively few trains making intermediate stops.
Germany on the other hand doesn't have such a dominant traffic generator and the existing agglomerations are dotted all around the country, so traffic is more spread out and it's more difficult to capture/speed up an appreciable fraction of that with just a few lines.