Go to reddit/r/personalfinance and you'll read lots of stories of people in shit jobs being taken advantage of by their employer. A society that allows people without money/education to be exploited is not a good one. In the U.S., from my perspective, we have a "I've got mine, fuck you" society. I'm not exploited at my job and I have a very comfortable existence. However, many of my fellow countrymen are not so fortunate.
Also, those restrictions on firing may be giving you a lot more potential employees. Changing jobs is a risk and if you were able to fire them after a week then that would be a major financial setback for them.
But this doesn't seem to be nearly enough to tip the balance in terms of operating a business overall ... I consistently hear from people how much it sucks to operate a small business in Europe. I don't see what's wrong in principle with having worker protections kick in at a certain company size, but that doesn't seem to be popular.
Of course, if your business is in maple syrup or something else with heavy government intervention, then your experience will likely be quite different. :)
If you think about companies as "us versus them", where "us" is workers and "them" is giant faceless monolithic corporations, then your idea that enforcing worker protections is a high priority might make sense.
But most companies are small. I run a software company ... I am just a guy trying to get by, who now in addition to the normal-person's burden of making my life go, has to also make a company go, and that company provides jobs for 10-12 people.
If you make my situation much harder than it is, the company would cease to exist or would downscale to 2-4 people, shedding the majority of the jobs. I am not a faceless corporation, I am just a guy who wants to get interesting things built. My little company is certainly not set up to "exploit workers", especially not on an industrial scale.
Now, paraxoically, if you add a lot more friction to what needs to happen to run a business (regulation around hiring, firing, invoicing, etc), then people like me drop out, and then what you mostly have left is the larger companies who do want to exploit workers because that is just kind of how larger companies work. Plus then you lose all the innovation / energy / economic activity that comes from smaller companies. It maybe seems like not the best idea. (If it is, how come Silicon Valley is not in France?)
As an investor, I fund a small French company and I have seen some of the crap they have to deal with just because they have a handful of employees. It makes me very glad I don't live in France.