Are secret quotas common in other settings? I don't think I've ever been told about one, and I had a whole lot of other jobs before starting this career.
I think it's a "damned if you do, damned if you don't" thing. If you make the law sweeping, businesses will complain it's an infringement of big government. If you make the law targeted, businesses will complain they're being unfairly selective.
What other industries do you think would benefit from this? Warehouse work might be unique enough to be afforded unique protections. There a lot of dark patterns you can employ against your workers in those settings, creating orders that are hard to fulfill on time, arranging your warehouse in ways that reduce worker productivity or even safety. Since many warehouses are moving consumer items and often food items there does seem to be reason to consider them separately from other industries.
They also have a separate labor union in many regions.
Well you wouldn't have been told about the secret quota, would you? But let's say you're right that it isn't common outside of warehouses. Even in that case, why would you write a law only for warehouses?
Let's say that there was a problem where cattle ranches were giving out beatings for underperforming workers. Would you fix this by writing a law that says "it is illegal for cattle ranches to beat employees" or would you just outlaw all beatings of all employees so that you won't have to revisit this when another industry decides to do it?