Ordinateur was not invented when computers came to the market. It was coined in its modern sense of computing machine, not by Proud French People Who Liked Their Language but by IBM France, because they felt that "calculateur" (French for -- whaddya know! -- "something that computes", a literal equivalent for "computer") was too restrictive. In the 1950s, when that happened, "ordinateur" had been in use for a very long time. I don't know how common it was (I'm not a native French speaker), but it's certainly not a word they made up on the spot (it's of very obvious Latin origin), and they don't use it because they don't have a more appropriate word for "computer" (which they do -- "calculateur", which they deemed inappropriate because a "calculateur" could do a lot more than "calculer"; just like, indeed, a "computer" could do a lot more than "compute").

Many European languages had a local equivalent for "computer" long before electronic computers were around, and French is certainly not the only one that kept it.