It's not an election, it's just one party choosing its candidate via an internal choice. There are plenty of parties in France, and plenty of candidates to vote for in the presidential election (6 or 7 already announced on the left, for instance).
Using the word "primary" was just a way to make it understandable as a concept, but it's not exactly the same process as in the USA. The roles of the various institutions are just so different form country to country, even (especially) in Europe, that it's hard to compare at times. In the long run, we're all dead. John Maynard Keynes
And I don't think it's strange that only party members in good standing pick a party candidate rather than have "primary election" open to anyone. Some states in the US do that by having a caucus system rather than a primary system. My state used to. In some ways it was better. You actually had to show up at party meetings and stand up and support someone. I'm not sure that they checked to make sure you'd payed your dues though. But I wouldn't have objected if they had.
