La Grève

Yeah, it was yesterday. But whatev (which rhymes with grève)
Yesterday, for no really good reason that I could see, everyone in the entire country was on strike. Not literally everyone, but it was national and for just one day. Even the local public park was "on strike" (closed for the day).
It makes very little sense to me, coming as I do from an American and not very labor-union-savvy background. But I was under the impression, and correct me if I'm wrong, that unions only used strikes for specific purposes, i.e. to accomplish something. I asked Madame why they were striking, and she looked at me like I was completely dense and said, "Because the economy's bad and they're not making enough money."
Yeah. Great. But did striking for one day and messing up countless people's lives who take the regional trains every day actually accomplish anything? Why do all the unions have to strike at once? Why, if they did accomplish something (a better contract, for example), did they strike at all or why didn't the strike last much longer?
Yes. I know. I'm being unreasonably demanding. There's no reason I should expect the French labor system to make any sense.
I'd just like to get your takes on it, too. Maybe I'm missing something.