Fast ebikes are classed as mopeds as such you'll have to use the roads and are banned from bicycle infrastructure. Pedelecs are classed as bikes and they're not limited to 25km/h, they just won't assist past that point. And frankly e-scooters at 20km/h are already plenty fast with those tiny wheels, ideally you don't want to drive faster than you can sprint and while athletes are faster (Usain Bolt sprints 44km/h), 20 is a good estimate for your average moderately out of shape human.

What's actually nuts about the speed limits 45km/h for mopeds and the like. 50km/h is ordinary city speeds and having people drive just a bit slower is inviting all kinds of unnecessary take-over manoeuvres.

Also just for completeness' sake there's plenty of speed limits for cars, also on the Autobahn, only about 57% are unlimited, 13% switch back and forth, unlimited doesn't mean unlimited and the safety record isn't bad in comparison to other countries. It could be improved but whether more limits would help is questionable.