good reason, like protecting homes

Don't know how it works where you live but here it's not just big zones, every building and plot has a designation (home, office, commercial, mixed residential + offices, commercial ground floor + residential above it), when you want to change the building or build a new one you need a building permit and ask the city for a change in designation, which they can deny.

We're terrible at urban planning, but that part I think does mean it's preventable.