Factually speaking, no one drives in first gear without gas in Germany either. But that's no different than the adherence to any other speed limit.
And of course it's painful, that's the point. You're supposed to avoid those 4-10km/h areas if at all possible. They're basically an admittance of "we couldn't technically forbid cars from entering". You'll never encounter them when shopping, going to church, or driving to the park.
We're just recently dropping speed limits in suburbs and more urban areas to 40 km/h and those school zones to 30 km/h.
I'm almost certain 4-10km/h is slower than idle in first gear in my manual diesel. That sounds painful, to be honest.