Why does it depend on each independent company, instead of just stating it by law? I mean, it seems that everybody across all industries should enjoy the same m

Why does it depend on each independent company, instead of just stating it by law? I mean, it seems that everybody across all industries should enjoy the same minimum sick days, not letting companies decide below that, because otherwise some (or most) will decide that number to be zero, as is the case. Otherwise these people will strike to gain some decency in their labor conditions, but it will be "wasted" effort in the sense that other industries will still lag behind with similar problems. Wouldn't it be better to have a more general change that applies to everybody? Companies are greedy, they'll always try to get as much as possible from their workers, if law allows for it. (note: not american. I'm just an observer from afar, in an european country where a lot of these worker rights are coded in the law; companies can offer perks above those rights, but never below)