Because in Europe ebikes are bikes with assistive motor, so you need to pedal and the motor just assists. So there is no throttle. And pedaling, even when it is easy, is an activity which consumes calories.
Another clarification... many of the higher-end e-bikes act as a power multiplier. If you put 100W into the pedals, you get 200W at the wheels (roughly). To go ~20mph, you're putting in ~15mph worth of effort. For my wife and I, that means she can keep up with me with a similar perceived exertion, which is really nice.
Some of the less expensive e-bikes just have a dumb switch on the pedal to meet legal requirements. You can barely pedal at all and the motor will accelerate to 20mph (or faster). And some have a throttle that bypasses the pedals completely (typically not allowed on bike trails/lanes, though hard to enforce).
"cycles with pedal assistance which are equipped with an auxiliary electric motor having a maximum continuous rated power of 0,25 kW, of which the output is progressively reduced and finally cut off as the vehicle reaches a speed of 25 km/h, or sooner, if the cyclist stops pedalling"
So, vehicles which do not require user to pedal, are not electric bicycles. Those are something else. Yes, it is legal to drive such vehicles, but those are not ebikes. Typically those vehicles require you to have an insurance, possibly type approval and maybe even drivers license, depending how fast they go and how powerful the motor is.
The very same limitations mentioned in the directive are in effect also in Germany. Bicycles with assistive motors up to 0.25 (nominal) kW and max assistive speed of 25km/h are effectively bicycles from law point of view. If the motor has more power and/or the max assistive speed is >25<45km/h, it's speed pedelec, not an electric bicycle. If the motor works without the rider pedaling at all, then it's a moped. The only difference here is that electric bicycles are in Germany called pedelec when pretty much rest of the world calls them ebikes.
Some of the less expensive e-bikes just have a dumb switch on the pedal to meet legal requirements. You can barely pedal at all and the motor will accelerate to 20mph (or faster). And some have a throttle that bypasses the pedals completely (typically not allowed on bike trails/lanes, though hard to enforce).