Like a lot of lawmakers they have no concept of how the internet works. They think it's like regulating cars (i.e. of course this handful of browser manufacturers will obey the law, so passing the law will control the behavior of the browsers).
They may think that even a ham-fisted law that doesn't match reality will give them some ability to control what non-tech-savvy citizens are able to see, and there may be some validity to that (although much less than they'd probably hope).
I don't think this is France's government right now, but certain governments can get a lot of mileage out of laws that are obviously impossible. In Russia, it's illegal to criticize the war, which is obviously impossible to enforce -- and yet, there are a bunch of people in prison, because they criticized the war and the government decided to single them out to be punished. It can be a ridiculous and impossible law; they're still in prison.