The problem is that there is a significant fraction of employers that pay for 40h (or whatever) and get more. And this is built-in into their current business plan (even if not explicitly). Their employees seem OK with it because they do it. But it's not easy to change into your situation: these employers either will have to pay more to get the hours they already get or pay the same but get less hours. This will have an impact on their cost structure. Whatever widgets they make will get more expensive.
This new regulation is the way the government is saying to these companies "yeah all this economic activity that you're doing is nice but we don't really want it actually. Not like this!"
Widgets that need to be more expensive, should.
> all this economic activity that you're doing is nice but we don't really want it actually. Not like this
That's what they said when we had 6day work weeks and went to 5, or when we got 40h work weeks. Actually enforcing it shouldn't be a bigger change than mandating it already was. Same thing with holidays. I make REALLY expensive widgets because I have 5weeks paid holiday. And they should be expensive because I really want the holiday.