Frances population is far more centered in mayor hubs while in Germany the population is dispersed much more homogeneous.
In some places the ICE stops every 20km, there are too many curves, or it shares its rails with slower trains.
There is no need for high speed rails here because you can not accelerate anyway.
"Looking forward rather than backward, nothing in Germany’s urban geography is an obstacle to a connected high-speed rail network. With central stations and less of the population living in truly isolated rural and small-city communities, Germany can expect to greatly surpass any other Western intercity rail network if it builds high-speed rail, more than reaching DB’s pre-corona 250 million ridership target."
Unfortunately there is no English Wikipedia page about it, but here is the German one: https://de.wikipedia.org/wiki/ICE_Sprinter